Difference between revisions of "Solutions to puzzles"

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=== Puzzle 2 ===
 
=== Puzzle 2 ===
−
Not posted yet...
+
 
 +
A winning move is Red e3. This connects to the top edge via [[Template IIIa]], and to the bottom edge via [[Edge template J5|Template J5]]. The two templates overlap at one point d3, but if Blue plays there, Red can reply f3 to seal the connection up and down.
 +
 
 +
<hexboard size="7x7"
 +
  coords="show"
 +
  contents="B c3 E *:d3 R 1:e3 B f5 R b6"
 +
  />
 +
 
 
=== Puzzle 3 ===
 
=== Puzzle 3 ===
  
Line 60: Line 67:
 
| 1. b4 || d2 || 2. d5 || c5 || 3. c4 || e3 || 4. d4 || e5
 
| 1. b4 || d2 || 2. d5 || c5 || 3. c4 || e3 || 4. d4 || e5
 
|}
 
|}
 +
 +
=== Puzzle 4 ===
 +
 +
<hexboard size="7x7"
 +
  contents="B f4 e4 d4 R f5 f2 1:c4"
 +
  />
 +
 +
Red 1. c4 is the only way to prevent Blue from connecting immediately by b5, c3 or c4. Red threatens to connect c4 to the top and bottom edges with assistance from the [[ladder escape]]s at f2 and f5.
 +
 +
Blue 2. c5 is met by Red 3. a6, which connects to the bottom edge with assistance from the ladder escape at f5 and threatens to connect to c4 or [[climbing|climb]] to  a4 and then connect to the top edge with assistance from the ladder escape at f2.
 +
 +
Blue may attempt a [[ladder escape fork]] by playing in the [[edge template]] between c4 and the top edge, but 2. c3 is met by 3. b4 and 2. c2 is met by 3. b3, which maintain the connection to the top edge and block Blue's ladder escape.
 +
 +
== Eric Demer ==
 +
 +
=== Puzzle 1 ===
 +
 +
The unique winning move is red a3.  a2 is captured to the top edge, and Red threatens b4.  e4 is a ladder escape, so b3 loses to a4 and b5 loses to b4.  b4 [[domination|capture-dominates]] a4 and a5. Thus Blue plays b4.
 +
 +
<hexboard size="5x5"
 +
  contents="R e4 a2 1:a3 B c3 b2 2:b4"
 +
  />
 +
 +
Red responds with e2. This connects to the bottom edge by [[edge template IV2d]], and connects to the top edge as shown.
 +
 +
<hexboard size="5x5"
 +
  contents="R e4 a2 1:a3 3:e2 5:d2 7:c2 9:b3 B c3 b2 2:b4 4:e1 6:d1 8:c1"
 +
  />
 +
 +
Uniqueness:
 +
 +
The shaded area is a [[virtual connection]] from c3, so Red must either play in it or play e2.
 +
 +
<hexboard size="5x5"
 +
  contents="R e4 a2 B c3 b2 S a5 b4 a4 a3 b2 b3 c2 c3"
 +
  />
 +
 +
The rest of this paragraph uses [[edge template III2a]] extensively, and so we do not mention it each time it's used.  If Red plays a5 or b4, then Blue plays b3, winning via d3 or e1.  If Red plays a4, then Blue plays c4, connecting left via a3 or a5.  a3 is Red's winning move.  If Red plays b3, then Blue plays c2, connecting left via a3 or b4.  If Red plays c2, then Blue plays c4, winning.
 +
 +
Red's only remaining try is e2.  Blue responds with c4.  After that, consider [[edge template III2a]] to the left edge.
 +
 +
<hexboard size="5x5"
 +
  contents="R e4 a2 1:e2 B c3 b2 2:c4 E *:b3 S a3 b3 a4 b4 a5 b5"
 +
  />
 +
 +
If Red [[Intrusion|intrudes]] there ''other than'' at ''*'', then Blue responding at ''*'' [[Captured cell|captures]] those 6 cells.  If Red [[Intrusion|intrudes]] at ''*'' ''before'' Red plays c2, then Blue responding at c2 still captures the template.    Thus, until Red has played c2, Red has no useful way of even ''threatening'' to disconnect c3 from the left edge, so one gets
 +
 +
<hexboard size="5x5"
 +
  contents="R e4 a2 1:e2 3:(d4 e3 d3) 5:d2 7:c2 B c3 b2 2:c4 4:e1 6:d1 8:c1"
 +
  />
 +
 +
At this point c3+c4 escapes the ladder from b2.
 +
 +
 +
=== Puzzle 2 ===
 +
 +
The unique winning move is blue d2.
 +
 +
<hexboard size="5x5"
 +
  contents="R d5 e1 B a2 1:d2"
 +
  />
 +
 +
This connects to the left edge via [[edge template IV2g]], so Red must play either in there or e2.  Against ''most'' [[Intrusion|intrusions]] in that template, Blue just responds with c3. Specifically, c3 ''almost'' makes this a [[second order template]], since even if Red starts with two moves in it, the only way Red can stop Blue from reconnecting is if those moves are in the two cells marked "*":
 +
 +
<hexboard size="5x4"
 +
  visible="-(a1 area(d3,b5,d5))"
 +
  edges="top left"
 +
  contents="B a2 d2 c3 E *:a4 *:b2"
 +
  />
 +
 +
Specifically, Red must have defended against b4.  If Red did that with b4 or a5, then Blue reconnects with b3 or c1.  Thus, Red needs a4.  Red must have also defended against b3.  If Red did that with b3 or a3, then Blue reconnects with c1.  Thus, Red also needs b2.
 +
 +
Since Blue c3 connects to the right edge via [[edge template III2b]], Red must play one of the shaded cells in the following diagram.
 +
 +
<hexboard size="5x5"
 +
  contents="R d5 e1 B a2 1:d2 S b2 a4 c3 e2"
 +
  />
 +
 +
Blue responds to e2 with d4.  Whether before or after that exchange, Blue responds to each of b2,a4 with b3.  At least two of b2,a3,a4 would still be empty, so that allows Blue to [[Climbing|climb]], for example like this:
 +
 +
<hexboard size="5x5"
 +
  contents="R d5 e1 B a2 B 1:d2 R 2:e2 B 3:d4 R 4:a4 B 5:b3 R 6:c3 B 7:c2 R 8:d3 B 9:b5"
 +
  />
 +
 +
Before the e2,d4 exchange, Blue responds to c3 with d4.  After the e2,d4 exchange, Blue can respond to c3 with d3.  In each case, Blue will have d2 and d4 [[Captured cell|captured]] to the right edge, so Red must defend against c1.  If Red does so with b2, then b3 is an [[Ladder escape fork|escape fork]] for the ladder from b5.  If Red does so anywhere else, then a2 still escapes that ladder.
 +
 +
Thus, both before and immediately after the e2,d4 exchange, none of Red's intrusions into the [[edge template IV2g]] work, so Red must try e2 followed by d3.  However, against that, Blue just plays b5, and ladders to a2.
 +
 +
<hexboard size="5x5"
 +
  contents="R d5 e1 2:e2 4:d3 B a2 1:d2 3:d4 5:b5"
 +
  />
 +
 +
Uniqueness:
 +
 +
Red's main threat is d3, bridging to [[edge template III2d]].  d2 is Blue's winning move.  e2 and d3 lose to c3, since d5 escapes the ladder.  d4 and c5 lose to b4, forming [[edge template IV2g]].
 +
 +
If Blue plays c4, then Red plays b4.  b4 will be [[Captured cell|captured]] to the bottom edge, so Blue must defend against c2.  c3 loses to b3, since e1 escapes the ladder. The other four all lose to d3.
 +
 +
This leaves just b5.  Red reponds with b4.
 +
 +
<hexboard size="5x5"
 +
  contents="R d5 e1 2:b4 B a2 1:b5"
 +
  />
 +
 +
That has a connection to the bottom edge, via a5 or c4, and threatens c2.  If Blue plays c4, then Red plays a5, [[Dead cell|killing]] b5 and thereby reverting to the "Blue plays c4, then Red plays b4" case.  If Blue [[Intrusion|intrudes]] in the other three cells of the connection from b4 to the bottom edge, then Red plays c4, re-establishing that connection and connecting to the top edge via [[edge template IV2a]].  Thus, Blue must defend against c2.  c3 loses to b3, since e1 escapes the ladder. The other four all lose to d3, since that connects via d4 or a5.
 +
 +
=== Puzzle 3 ===
 +
 +
The unique winning move is blue b2.
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 B d1 1:b2"
 +
  />
 +
 +
That [[Captured cell|captures]] a2 and a3, and threatens e1, so Red must play in c1,c2,e1.  The b2-d1 bridge is [[Bolstered template|bolstered]] at c1 ([[Equivalent patterns#Edge equivalence|by Red's edge]]), so c1 is now worse than c2.
 +
 +
If Red plays c2, then Blue plays d2.  That captures e1 and e2, so Red must respond with c1.  Blue then plays b4, which connects left via e5 or b3, and connects right via [[edge template IV2e]].
 +
 +
Thus Red plays e1.  Blue responds with e2.
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:e1 B d1 1:b2 3:e2"
 +
  />
 +
 +
Red must play in c1,c2,e1.  As before, we discard c1.  If Red plays c2, then Blue plays d2, [[Dead cell|killing]] e1 and thereby reverting to the "Red plays c2, then Blue plays d2" case.  Thus Red plays d2.  Blue responds with c4, connecting left via a5 or c3 and connecting right via e3 or d5.
 +
 +
Uniqueness:
 +
 +
I use it twice here, in already-dense prose, so I start with what I will call "the c4 ziggurat-defense":
 +
 +
If Blue plays in the e3 ziggurat ''other than'' at c4, then Red can respond at c4, after which Red can keep ''both'' c4 and e3 connected down inside the ziggurat:  Either c4 is captured down, in which case e3 connects via one of {d3,d4,e4}, or Red can defend the bridge, in which case c4+e3 connects down via one of {b5,c5,e4}.
 +
 +
With that out of the way, suppose Blue plays anywhere other than the five cells marked "*" in the following diagram.
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 B d1 E *:(c1 b1 b2 c4 a5)"
 +
  />
 +
 +
Red responds with b2, [[Captured cell|capturing]] b1 and c1.  Blue gets one more move before it becomes Red's turn again, and Blue's two moves can't be Blue occupying ''both'' c4 and a5.
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:b2 c1 b1 B d1 E *:c4 *:a5"
 +
  />
 +
 +
One of Blue's two moves must be in {a5,a3,b3}, and the other of Blue's two moves must defend against d2, since red d2 would connect down via [[edge template IV2i]].
 +
 +
If that other move from Blue is not in the e3 ziggurat, then Red wins by laddering to e3:  If Blue played a5 then Red plays b4, else Red defends the a4-b2 bridge.
 +
 +
If Blue played in the e3 ziggurat ''other than'' at c4, then Red uses the c4 ziggurat-defense, after which Red wins with d2 or the ladder along the bottom.  Thus, one of Blue's two moves must be c4.  This means Blue's other move can't be a5, so it must have been a3 or b3, to defend against red a5.  In either case, Red plays b4, winning via either d2 or the other of a3,b3.
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:b2 4:b4 6:d2 B d1 1:b3 3:c4 5:a3"
 +
  />
 +
 +
Thus, Blue must have played one of the five cells marked "*" in the following diagram.
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 B d1 E *:(c1 b1 b2 c4 a5)"
 +
  />
 +
 +
b2 is Blue's winning move, and against the other four, Red plays d2.
 +
 +
If Blue has played b1 or c1, then we claim that the entire red-shaded region below is captured by Red:
 +
 +
<hexboard size="5x5"
 +
  edges="all"
 +
  coords="top left"
 +
  contents="R a4 e3 2:d2 B d1 E *:(b1 c1) S red:-(e1 area(d1,b3,a3,a1))"
 +
  />
 +
To prove this, it is sufficient to show that Red has a strategy in the shaded region that keeps both a4 and d2 connected to the bottom edge. Because by the time the board is completely filled, if a4 and d2 are connected to the bottom edge, no minimal blue winning path can pass through the shaded area. Therefore all blue stones in that area will be dead.
 +
 +
To show that a4 and d2 are simultaneously connected down, consider any blue move in the region. If Blue plays b4, then Red responds with a5.  In that case, d2 still connects down via [[edge template IV2i]]. Thus, Blue tries somewhere else in this region.  Red responds at b4, and Blue gets one more move before it becomes Red's turn again.
 +
 +
If Blue's two moves were a5 and b5, then Red plays d4, connecting both d2 and b4 to the bottom with a [[trapezoid]]. Otherwise, Blue played at most one of a5,b5.  If Blue played exactly one of those two, then Red plays the other, killing whichever of those two was Blue.  In that case, Blue again gets one more move before it goes back to being Red's turn, so for showing this capture, we are left with the case where neither of Blue's was was in {a5,b5}.  Since b4 is red, a5 and b5 are directly red-captured, so one of Blue's two moves must be c3, since otherwise Red plays there.  The order in which Blue played Blue's two moves doesn't matter, so one can pretend Blue played c3 first.  In that case, before Blue played Blue's other move, Red had a bridge to e3 and a connection from e3 due to the ladder escape at b4.  Thus, Red can respond to restore the connection down from d2.
 +
 +
Due to this capture, the positions simplify to the following,
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:d2 c3 b4 a5 B d1 S blue:(b1 c1)"
 +
  />
 +
 +
where the shading indicates that one of b1,c1 is blue and the other is empty.
 +
 +
Blue must play e1. After that, if c1 is empty, Red plays at c1 and is connected by a [[crescent]], and if b1 is empty, Red plays at a2 and is connected by a different crescent and [[edge template II]]. This shows that both 1. b1 and 1. c1 are losing for Blue.
 +
 +
The remaining moves for Blue are a5 and c4. If Blue plays a5, then we claim that within the red-shaded region in the following diagram, Red can keep d2 connected down while ensuring that red b4 would connect down.
 +
<hexboard size="5x5"
 +
  edges="all"
 +
  coords="top left"
 +
  contents="R a4 e3 2:d2 B 1:a5 d1 S red:-(e1 area(d1,b3,a3,a1))"
 +
  />
 +
The proof is similar to our proof of capture above. Specifically, before Blue plays there, d2 has a template down and red b4 would connect down since e3 escapes the ladder.  If Blue plays b4, then red b4 can't happen and d2 still connects down, since b4 isn't in [[Edge template IV2i|the template]].  If Blue plays c3, then Red plays d4, capturing d2 down and guaranteeing a ladder escape for red b4.  The d2-e3 bridge is [[Bolstered template|bolstered]] at e2, so e2 is worse than d3.  If Red plays in the e3 ziggurat ''other than'' at c4, then Red uses the c4 ziggurat-defense, after which d2 connects down via c3 or e2, and red b4 would also connect down.  If Blue plays c4, then Red plays d4.  That captures d2 down, so red b4 would connect down via b5 or c3.
 +
 +
Given that, Red wins as follows:
 +
<hexboard size="5x5"
 +
  edges="all"
 +
  contents="R a4 e3 2:d2 4:b2 6:b4 B 1:a5 d1 3:e1 5:c2 S red:-(e1 area(d1,b3,a3,a1))"
 +
  />
 +
 +
Thus​ 1. a5​ loses, so Blue's only remaining try is ​1. c4.
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:d2 B d1 1:c4"
 +
  />
 +
 +
Red threatens
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:d2 4:c2 B d1 1:c4 S a5 b5 b4 b3 c3 c2 c1 e1 e2 d3 d5 e5 e4"
 +
  />
 +
 +
and
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:d2 4:b2 B d1 1:c4 S a5 a3 b3 b2 b1 c1 c2 e1 e2 d3 d4 d5 c5"
 +
  />
 +
 +
so Blue must play one of the cells shaded below.
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:d2 B d1 1:c4 S a5 b3 c2 c1 e1 e2 d3 d5"
 +
  />
 +
 +
If Blue plays in {d5,d3,e2}, then Red plays b4, which captures a5 and b5, so Blue must defend against b2.  Blue playing in {a3,b2,b1} loses to c2, Blue playing c1 loses to b3 - threatening e1 and a2 - and Blue playing b3 loses to b2, since that connects d2 to the top via e1 or c2.
 +
 +
If Blue plays e1 or c2, then Red plays
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:d2 4:b2 6:a3 8:b4 10:d4 B d1 1:c4 5:b3 7:a5 9:b5 11:c3 S blue:(c2 e1)"
 +
  />
 +
 +
and then wins with whichever of e1,c2 Blue did not play.
 +
 +
If Blue plays c1, then Red plays b3 and defends that bridge.  That connects to the top with a2 or e1 and to the bottom with a5 or d4.
 +
 +
If Blue plays b3, then Red plays b2.  That captures b2 and d2 to the top, so Red wins with b4 or d4.
 +
 +
Lastly, if Blue plays a5, then Red wins as follows.
 +
 +
<hexboard size="5x5"
 +
  contents="R a4 e3 2:d2 4:d4 6:b2 8:b4 10:c3 B d1 1:c4 3:a5 5:e1 7:c2 9:b5"
 +
  />
 +
 +
=== Puzzle 4 ===
 +
 +
Uniqueness:
 +
 +
Blue's main threat is c2, bridging to [[edge template III2a]].
 +
 +
<hexboard size="5x5"
 +
  contents="R e5 a1 B e1 c1 2:c2 S b1 a2 b2 a3 b3 a4 c2 d2 d1"
 +
  />
 +
 +
If Red plays in {b1,b2,a2,a3}, then Blue plays b4, and wins with [[edge template IV2g]].  If Red plays a4, then Blue plays b2, and wins with d1 or c3.
 +
 +
If Red plays b3 or c2, then Blue plays b2, forcing d1.
 +
 +
<hexboard size="5x5"
 +
  contents="R e5 a1 3:d1 B e1 c1 2:b2 4:c3 S red:(b3 c2)"
 +
  />
 +
 +
Blue continues with c3.  This connects right via [[edge template III2d]], and connects left with c2 or b3 or b4.
 +
 +
If Red plays d1, then Blue plays c3.  That connects right with [[edge template III2d]] and connects left with a ziggurat.
 +
 +
There is only 1 remaining try for Red, and that is Red's winning move: d2
 +
 +
Showing that d2 wins for Red:
 +
 +
This part is quite similar to showing that d2 wins for Blue in [[Solutions to puzzles#Puzzle 2_2|puzzle 2]].
 +
 +
<hexboard size="5x5"
 +
  contents="R e5 a1 1:d2 B e1 c1"
 +
  />
 +
 
 +
The following region is a [[virtual connection]]:
 +
 +
<hexboard size="5x5"
 +
  visible="-(e1 area(d1,a1,a4))"
 +
  edges="bottom right"
 +
  coords="bottom right"
 +
  contents="R e5 d2"
 +
  />
 +
 +
d3 fails to c3, since e5 escapes the ladder, c3 and c4 fail to e3, forming [[edge template III2d]], and everything else fails to c4, connecting down via one of b5,c5,d4.
 +
 +
Against ''most'' [[Intrusion|intrusions]] in that [[virtual connection]], Red just responds with c3.  Specifically, c3 ''almost'' makes this a [[Second order template|second order]] connection, since even if Blue starts with two moves in it, the only way Blue can stop Red from reconnecting is if those moves are in the two cells marked "*":
 +
 +
<hexboard size="5x5"
 +
  visible="-(e1 area(d1,a1,a4))"
 +
  edges="bottom right"
 +
  coords="bottom right"
 +
  contents="R e5 d2 c3 E *:b5 *:d4"
 +
  />
 +
 +
Specifically, Blue must have defended against b4.  Blue's other move must have been in {c4,d4,d3}, since otherwise Red plays d4 and connects with one of c5,d5,e4.  d3 fails to c4, since e5 escapes the ladder, and c4 fails to e3, forming [[edge template III2d]], so Blue's other move must be d4.  This means a5 and b4 fail to c4, so Blue also needs b5.
 +
 +
Since red c3 connects to the top via d1 or b2, Blue must play one of the shaded cells in the following diagram.
 +
 +
<hexboard size="5x5"
 +
  contents="R e5 a1 1:d2 B e1 c1 S d1 c3 b5 d4"
 +
  />
 +
 +
Red responds to d1 with b2.  Whether before or after that exchange, Red responds to each of b5,d4 with c4.  c4 would connect down - via b5 or c5 or laddering to e5 - so that allows Red to [[Climbing|climb]], for example like this:
 +
 +
<hexboard size="5x5"
 +
  contents="R e5 a1 1:d2 3:b2 5:c4 7:d3 9:a4 B e1 c1 2:d1 4:b5 6:c3 8:c2"
 +
  />
 +
 +
Before the d1,b2 exchange, Red responds to c3 with b2.  After the d1,b2 exchange, Red can respond to c3 with c2.  In each case, Red will have b2 and d2 [[Captured cell|captured]] to the top edge, so Blue must defend against both e3 - forming [[edge template III2d]] - and the [[ladder escape fork]] at c4.
 +
 +
<hexboard size="5x5"
 +
  visible="-(a2 c2 line(a1,e1))"
 +
  edges="bottom right"
 +
  coords="bottom right"
 +
  contents="R e5 a1 1:d2 b2 B c3 S d3 c5"
 +
  />
 +
 +
The overlap between those threats is {d3,c5}.  Against d3, Red plays a4 and ladders to e5.  Against c5, Red plays b5, followed by a4 or d3.  (d3 connects with c4 or either of d4,e4).
 +
 +
Thus, both before and immediately after the d1,b2 exchange, none of Blue's intrusions into
 +
 +
<hexboard size="5x5"
 +
  visible="-(e1 area(d1,a1,a4))"
 +
  edges="bottom right"
 +
  coords="bottom right"
 +
  contents="R e5 d2"
 +
  />
 +
 +
work.  Since b2 will be captured to a1, this means Blue must try d1 followed by c2.  However, against that, Red just plays a4, and ladders to e5.
 +
 +
<hexboard size="5x5"
 +
  contents="R e5 a1 1:d2 3:b2 5:a4 B e1 c1 2:d1 4:c2"
 +
  />
 +
 +
=== Puzzle 5 ===
 +
 +
To find Red's winning move, let's use [[Mustplay region|mustplay analysis]] to narrow down the possibilities. Blue has several [[threat]]s, which are shown with their respective [[carrier]]s:
 +
 +
[[Bridge]] to [[ziggurat]]:
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 B b5 e1 B 1:c2 S d1,area(d2,a2,a5)"
 +
  />
 +
 +
b4 and [[double threat]]:
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 B b5 e1 B 1:b4 E *:d4 *:c2 S area(a5,c5,e4,e3,c4,d2,d1,a4)"
 +
  />
 +
 +
b4 and a different [[double threat]]:
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 B b5 e1 B 1:b4 E *:d4 *:c2 S area(a5,c5,e4,e3,c4,d2,d1,a2,a3,e2,a4)"
 +
  />
 +
 +
Ladder and climbing from b2:
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 B b5 e1 B 1:d4 R 2:a5 B 3:b4 R 4:a4 B 5:b2 S area(e4,c5,a5,a2,c1,d1,a4,e3)"
 +
  />
 +
 +
c4 with [[edge template III2b]] and ladder:
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 B b5 e1 B 1:c4 R 2:d4 B 3:d3 R 4:e3 B 5:d2 S area(a3,a5,e5,e3,d2)"
 +
  />
 +
 +
Red must play in the intersection of these carriers, i.e., at a4, a5, or b4.
 +
 +
Red a4 loses to Blue c3, with double threats towards both edges:
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 B b5 e1 R 1:a4 B 2:c3 E *:a5,b2,d4,d2"
 +
  />
 +
 +
Red a5 loses to Blue c2 as follows. Apart from [[intrusion|attacking]] Blue's bridge, which Blue can simply defend, Red's moves 3 and 5 are forced, after which Blue wins by double threat:
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 B b5 e1 R 1:a5 B 2:c2 R 3:a3 B 4:a4 R 5:b3 B 6:b4 E *:c3,d4"
 +
  />
 +
 +
This leaves b4 as the only possible move for Red.
 +
 +
Showing that b4 wins for Red:
 +
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 1:b4 B b5 e1"
 +
  />
 +
 +
If Blue plays to the upper-left of the [[short diagonal]] ''other than'' in {c2,b3}, then Red responds with c2 and defends the bridge.  c2 connects to the top via d1 or c1 or b2, and connects to the bottom with a very short [[switchback]].
 +
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 1:b4 3:c2 5:b3 7:d4 9:d2 B b5 e1 2:a3 4:c3 6:a5 8:c4"
 +
  />
 +
 +
If Blue plays to the lower-right of the [[short diagonal]] ''other than'' at d4, then Red plays a5.  This threatens c2, which would connect to the top via d1 or c1 or b2, so Blue must respond in {c2,c3,b3}.  If Blue plays c2 or c3, then Red plays a3, winning with [[Edge template III2d]].  Thus Blue plays b3 instead.  Red responds with d2, and a1 escapes that ladder.
 +
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 1:b4 3:a5 B b5 e1 S blue:(d3 e3 e4 e5 d5 c5 c4)"
 +
  />
 +
 +
Blue must continue with c3, and what's left of this case is checking that Red can connect e2 down no matter which of the above shaded cells was Blue's first move.  If that move was neither d3 nor e3, then Red bridges to d4, and connects down with c4 or c5 or d5.  Otherwise, Red plays whichever of d3,e3 Blue didn't play.  Since Red has a5 and b4, b5 is [[Dead cell|dead]], so Red ladders to b4.
 +
 +
If Blue plays d4, then Red plays c4, capturing a5 and c5.  This threatens c2, which would connect to the top via d1 or c1 or b2, so Blue must respond in {c2,c3,b3}.  If Blue plays c2 or c3, then Red plays a3, winning with [[Edge template III2d]].  If Blue plays b3, then Red plays d2, bridging from c4 and laddering to a1.
 +
 +
This leaves the following tries for Blue.
 +
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 1:b4 B b5 e1 S d2 c2 c3 b3 a5"
 +
  />
 +
 +
c2 loses to a3, using [[Edge template III2d]]
 +
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 1:b4 3:a3 5:d4 7:d2 B b5 e1 2:c2 4:a5 6:c4"
 +
  />
 +
 +
and a [[switchback]], as shown above.
 +
 +
If Blue plays b3, then Red plays d2, and a1 escapes that ladder.  Towards the bottom, if Blue plays outside of {c4,c3,d3}, then Red can play c4 and defend the bridge from d2, and if Blue plays outside of {d4,d5,c5}, then Red can play d4 and defend the c5+d5 [[Captured cell|capture]].
 +
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 1:b4 3:d2 B b5 e1 2:b3"
 +
  />
 +
 +
In the former case, Red connects down with a5 or c5 or e4.  In the latter case, Red connects down with e3 or d3 or c3, since c3 threatens c4 and a5.  The sets {c4,c3,d3} and {d4,d5,c5} are disjoint, so Red gets at least one of those, and thereby connects down for a win.
 +
 +
If Blue plays c3, then Red plays d4, capturing e2 and b4 to the bottom.  Blue must respond in {d2,c2,b3}, since otherwise Red plays c2, connecting down with d2 or b3 and connecting to the top with d1 or c1 or b2.  If Blue plays d2 or c2, then Red plays a3, winning with [[Edge template III2d]].  If Blue plays b3, then Red plays d2, and wins by laddering to a1.
 +
 +
If Blue plays d2, then Red plays c3, connecting down with a5 or d4.  Towards the top, blue c2 loses to a3, forming [[Edge template III2d]], and Blue's other moves all lose to red c2, connecting with d1 or c1 or b2.
 +
 +
Blue's only remaining try is a5.  Red responds to that with d4, [[Captured cell|capturing]] c5 and d5.
 +
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 1:b4 3:d4 c5 d5 B b5 e1 2:a5"
 +
  />
 +
 +
Red's main threat is d4, laddering to a1.
 +
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 1:b4 3:d4 c5 d5 5:d2 B b5 e1 2:a5 S a2 b1 b2 c1 c2 d1 d2 d3 e3"
 +
  />
 +
 +
If Blue plays in {a2,b1,b2,c1,d1}, then Red plays c2.  This connects to the top with d1 or c1 or b2, and connects down with a [[Interior template#The box|box]].
 +
 +
If Blue plays c2, then Red plays d2.  This connects down with a [[trapezoid]], and connects to the top with d1 or a3, since a3 forms [[Edge template III2d]].
 +
 +
If Blue plays d2, then Red plays c3.  This has a bridge down, and connects to the top for the same reason as without the a5-b4 exchange.
 +
 +
The e2-d4 bridge is [[Bolstered template|bolstered]] at e3 ([[Equivalent patterns#Edge equivalence|by Blue's edge]]), so e3 is no better for Blue than d3.
 +
 +
Thus, the only remaining case is ​ ​ ​ 4. d3 ​ .
 +
 +
<hexboard size="5x5"
 +
  contents="R e2 a1 1:b4 3:d4 5:c4 c5 d5 B b5 e1 2:a5 4:d3"
 +
  />
 +
 +
Against that, Red plays ​ ​ ​ 5. c4 ​ .
 +
 +
This threatens c2, which would connect to the top via d1 or c1 or b2, so Blue must respond in {c2,c3,b3}.  If Blue plays c2 or c3, then Red plays a3, winning with [[Edge template III2d]].  Thus Blue plays b3 instead.  Red responds with d2, connecting down via c3 or e3, and connecting to the top because a1 escapes the ladder.
 +
 +
Therefore ​ 1. b4 ​ does win for Red.
 +
 +
=== Puzzle 6 ===
 +
The unique winning move is c4. In the follow-up, Black must play d3 to get [[edge template IV2b]]::
 +
<hexboard size="6x6"
 +
  coords="show"
 +
  contents="R a3 b2 B d1 e1 f1 R 1:c4 B 2:b3 R 3:a4 B 4:b5 R 5:d3"
 +
  />
 +
 +
=== Puzzle 7 ===
 +
The unique winning move is c6:
 +
<hexboard size="7x7"
 +
  coords="show"
 +
  edges="all"
 +
  contents="R g3 g2 e5 e3 c5 b5 a2 B d7 e4 d5 c4 b4 B 1:c6"
 +
  />
 +
Indeed, now Blue is connected left by double threat at d4 or b6, and right by f6 or a [[ladder escape fork]] from f4. The uniqueness of the winning move is discussed in more detail in the article on the [[Mustplay_region#Solving_Hex_puzzles|mustplay region]].
  
 
== Other authors ==
 
== Other authors ==
  
 
=== Puzzle 1 ===
 
=== Puzzle 1 ===
−
Not posted yet...
+
There are two main solutions. In the first line, Blue at (*) on move 7 or 9 is also winning.
 +
<hexboard size="10x10"
 +
  coords="show"
 +
  contents="R i1 h4 g5 f6 d9 c8 B g4 f5 e6 d7
 +
            B 1:h3 R 2:j2 B 3:i3 R 4:j3 B 5:i4 R 6:j4 B 7:h8 R 8:i6 B 9:g7 E *:e8"
 +
  />
 +
 
 +
In the second line, Blue has several winning moves starting move 9, but we show just one example.
 +
<hexboard size="10x10"
 +
  coords="show"
 +
  contents="R i1 h4 g5 f6 d9 c8 B g4 f5 e6 d7
 +
            B 1:g8 R 2:h7 B 3:h3 R 4:j2 B 5:i3 R 6:j3 B 7:i4 R 8:j4 B 9:i5 R 10:j5
 +
            B 11:i6 R 12:j6 B 13:i8 R 14:i7 B 15:f9
 +
"
 +
  />
 +
 
 +
Surprisingly, these are the only winning first moves for Blue. For example, 1. h8 is a losing move, but the refutation is subtle and depends on play in the lower-left obtuse corner:
 +
<hexboard size="10x10"
 +
  coords="show"
 +
  contents="R i1 h4 g5 f6 d9 c8 B g4 f5 e6 d7
 +
            B 1:h8 R 2:i4 B 3:i2 R 4:h3 B 5:h2 R 6:g3 B 7:g2 R 8:f3 B 9:f2 R 10:e3
 +
            B 11:e2 R 12:c3 B 13:d3 R 14:c4 B 15:d4 R 16:b6 B 17:c7 R 18:a8 E *:d8
 +
"
 +
  />
 +
 
 +
However, Red's refutation fails when Blue plays 1. g8 instead, because after Red 12, Blue can instead play 13. d8! at (*), which threatens to connect to g8 (which wouldn't have been possible had Blue started with 1. h8).
  
 
=== Puzzle 2 ===
 
=== Puzzle 2 ===
−
Not posted yet...
+
Note that Red is connected upwards by [[Edge_template_J5|Template J5]]. The only way to prevent Red from connecting downwards is to play in the cell marked (*).
 +
<hexboard size="7x7"
 +
  coords="show"
 +
  contents="R b2 B e3 R b5 E *:b6"
 +
  />
 +
Perhaps surprisingly, (*) is a winning move, while any intrusion into the template on the first move is losing.
 +
If Red responds as expected at 2.c5, Blue's response is to intrude Red's upward connection at 3.b4. This leaves Blue in a strong position.
 +
<hexboard size="7x7"
 +
  coords="show"
 +
  contents="R b2 B e3 R b5 B 1:b6 R 2:c5 B 3:b4"
 +
  />
 +
If Red instead plays 2.g4, Blue can respond with 3.d5, again leaving Blue in a strong position.
 +
<hexboard size="7x7"
 +
  coords="show"
 +
  contents="R b2 B e3 R b5 B 1:b6 R 2:g4 B 3:d5"
 +
  />,
 +
Other possible moves by Red also have a strong response, for example 2.c6 3.c4, or 2.d4 3.d5, or 2.d5 3.c4, or 2.e4 3.e5.
 +
 
 +
=== Puzzle 3 ===
 +
 
 +
To simplify the analysis, it helps to note that because c9 connects to the left and a3 connects to the top, the left and top areas of the board are completely [[settled region|settled]]. Moreover, i2 [[captured cell|captures]] j1 and j2 and [[dead cell|kills]] h3, which in turns captures i3 and j3. Additionally, f6 and g5 are captured by Red. Therefore, the situation of the puzzle is [[equivalent patterns|equivalent]] to the following:
 +
<hexboard size="10x10"
 +
  coords="show"
 +
  contents="B area(b1,b3,j3,j1) R area(a1,a4) B area(a5,a10,c10,d9,d5) R f6 g5
 +
R a3 e3 f3 g3 a4 b4 c4 e4 g4 h4 c5 d5 f5 e6 e7
 +
B e2 f2 g2 h2 i2 b3 d3 d4 f4 b5 e5 d6 g8 c9 d9"
 +
  />
 +
Therefore, whatever Red can do, Red must do in the lower right corner. Here is how Red can win:
 +
 
 +
<hexboard size="10x10"
 +
  coords="show"
 +
  contents="S red:area(a1,a2) blue:area(b1,b2,c3,e1),e1--j1--j3--h3
 +
            blue:area(a5,a10,d8,d7,c6),b10,c10 red:f6,g5
 +
R a3 e3 f3 g3 a4 b4 c4 e4 g4 h4 c5 d5 f5 e6 e7
 +
B e2 f2 g2 h2 i2 b3 d3 d4 f4 b5 e5 d6 g8 c9 d9
 +
R 1:e9 3:f8 5:g7 7:i5 9:j6
 +
B 2:e8 4:f7 6:g6 8:h6"
 +
  />
 +
 
 +
=== Puzzle 4 ===
 +
 
 +
To simplify the analysis, it helps to note that Blue's g2 [[group]] is already connected to the right edge (see below), and Red's c6 group is already connected to the bottom edge. Moreover, Blue does not have any prospects for escaping a 2nd row ladder approaching the lower left from under c6. For these reasons, the position in the puzzle is [[equivalent patterns|equivalent]] to the following:
 +
 
 +
<hexboard size="10x10"
 +
  coords="show"
 +
  contents="R area(c6,a8,a10,j10,j6) B area(h1,f3,e5,j5,j1)
 +
R b4 e4 c6 d7 d8
 +
B b2 g2 f3 f4 e5
 +
"
 +
  />
 +
 
 +
Therefore, everything Blue can do must be done in the upper left corner. The winning move is c4:
 +
 
 +
<hexboard size="10x10"
 +
  coords="show"
 +
  contents="
 +
S red:area(c6,a8,a10,j10,j6) blue:area(h1,f3,e5,j5,j1)
 +
R g3 b4 e4 c6 d7 d8
 +
B b2 g2 f3 f4 e5
 +
B 1:c4
 +
"
 +
  />
 +
Blue 1. c4 threatens to connect left by b5 or c3 and right by d5, d4 or e3. If Red replies in the region a2-c2-c4-a6, other than at c3, to threaten c4's connection left, then Blue 3. c3 connects to the left edge, and to the right via e2 or d5.  The only reply outside the region a2-c2-c4-a6 that prevents the group of 4 blue pieces connecting immediately to the left edge by d5, d4 or e3 is Red 2. d4. However, Red 2. d4 and 2. c3 can be answered by 3. e2.
 +
 
 +
To see why Blue's g2 group is connected right, Blue's main [[threat]]s are 1. g5, connecting via [[Edge template IV1d]] and by the [[ladder escape fork]] 1. i1 2. j1 3. i3 4. i2 5. g4.  Red can only meet both these threats by playing in overlap of these templates, in the marked cells.
 +
 
 +
<hexboard size="10x10"
 +
  coords="show"
 +
  contents="
 +
R g3 b4 e4 c6 d7 d8
 +
B b2 g2 f3 f4 e5
 +
E *:line(g4,h4,j2,j3)
 +
"
 +
  />
 +
 
 +
However these replies can be met by:
 +
 
 +
2. i3 3. i2 4. h2 5. g4 6. h3 7. h5
 +
 
 +
2. j3 3. i2 4. h2 5. g4 6. h3 7. h4 8. i3 9. i5
 +
 
 +
2. g4 3. i1 4. j1 5. i2 6. j2 7. i3 8. j3 9. i5 10. i4 11. h5 12. h4 13. f6
 +
 
 +
2. h4 then either 3. g4 threatening 5. i2 and 5. g6 - or simply 3. i2 4. h2 5. g4 6. h3 7. g6 - forming a [[crescent]] and connecting with the assistance of the second row [[ladder escape]] at i2
 +
 
 +
2. j2 3. h2 4. i2 ([[Dominated_cell#Capture-domination|capture-dominates]] the alternatives i1 & j1) 5. h5 - a double [[ziggurat]] connection
 +
 
 +
[Note that although we used [[Edge template IV1d]] from g5 in the above explanation to minimise the overlap and the resulting case analysis, we don't need the whole template or the method of connection used for that.  If however we use the smaller and simpler [[Edge template IV1a]] from g5, then the overlap with the ladder escape fork template is larger and we need to consider the additional replies h3, i2 and j1 (although j1 is [[Dominated_cell#Capture-domination|capture-dominated]] by i2, so any winning variations against i2 also work against j1).  Although 3. g5, connecting via Edge template IV1d, works against all these replies, there are simpler and quicker responses, e.g.: 2. h3 3. i4; 2. i2 3. h3 4. i3 5. h5 or 4.j3 5. i5; 2. j1 3. i3.  So the analysis above only demonstrates that Blue is connected, rather than showing the smallest connection template or the quickest or simplest method of connection.]
  
 
=== Puzzle 5 ===
 
=== Puzzle 5 ===
−
part 1:
+
Red's [[mustplay region]] consists of these 8 cells, because if Red plays anywhere else, Blue plays at d4 and wins immediately.
−
<hexboard size="11x11"
+
<hexboard size="6x6"
 
   coords="show"
 
   coords="show"
−
   contents="B h2 R a4 R b5 R c6 B 3:d7 B e7 R 4:b8 B g8 R b9 R 2:c9 R 8:e9 R 10:f9 B 1:b10 R 6:c10 B 9:e10 B 7:b11 B 5:c11"
+
   contents="R a4 a6 B a5 b5 S red:(c4 c5 d4 e3 e4 f2 f3 f4)"
 
   />
 
   />
−
part 2:
+
The unique winning move is Red c4. Red then connects for example like this:
−
<hexboard size="11x11"
+
<hexboard size="6x6"
 
   coords="show"
 
   coords="show"
−
   contents="B h2 R a4 R b5 R c6 R 10:j6 B d7 B e7 B 9:i7 R 6:j7 R b8 B g8 B 7:i8 R 8:j8 R b9 R c9 R e9 R f9 R 2:g9 B 5:h9 R 4:i9 B b10 R c10 B e10 B 1:f10 B 3:g10 B b11 B c11"
+
   contents="R a4 a6 B a5 b5 R 1:c4 B 2:c5 R 3:e4 B 4:d3 R 5:f2 B 6:f1 R 7:e2 B 8:e1 R 9:d2 B 10:d1
 +
            R 11:b2 B 12:c2 R 13:b4"
 
   />
 
   />
−
part 3:
+
 
−
<hexboard size="11x11"
+
Another move that looks plausible is Red d4, but it fails to this:
 +
<hexboard size="6x6"
 
   coords="show"
 
   coords="show"
−
   contents="B h2 R 2:j2 R a4 R b5 B 1:g5 R c6 R j6 B d7 B e7 B 3:f7 B i7 R j7 R b8 B g8 B i8 R j8 R b9 R c9 R e9 R f9 R g9 B h9 R i9 B b10 R c10 B e10 B f10 B g10 B b11 B c11"
+
   contents="R a4 a6 B a5 b5 R 1:d4 B 2:e5 R 3:c6 B 4:d3 R 5:c4 B 6:c3 R 7:b4 B 8:b2"
 
   />
 
   />
 +
 +
=== Puzzle 6 ===
 +
The unique winning move is b7. In the following line, Red's moves below (1, 3, 5, and 7) are the only moves that preserve the win. Note that moves 1 and 3 are [[minimax|minimaxing]] moves, while move 7 is a [[foiling]] move that blocks the ladder escape created from Blue 6.
 +
<hexboard size="13x13"
 +
  coords="show"
 +
  contents="R a3 h3 g4 h5 g6 i6 c7 i7 j7 g8 k8 h9 k9 d10 i10 k11
 +
            B i2 g3 i3 d4 j4 j6 f7 g7 h7 h8 i8 i9 j9 l9 j10 k10
 +
            R 1:b7 B 2:e7 R 3:d7 B 4:d8 R 5:c9 B 6:c10 R 7:b10"
 +
  />
  
 
== See Also ==
 
== See Also ==
Line 91: Line 694:
  
 
[[category:Puzzle]]
 
[[category:Puzzle]]
−
{{stub}}
 

Latest revision as of 14:12, 25 August 2024

Piet Hein

See Solutions to Piet Hein's puzzles

Claude Berge

See Solutions to Claude Berge's puzzles

Bert Enderton

Puzzle 1

The unique winning first move is Red b4. (Blue can easily defend the bridges at e3/e4 and g2/g3. Red d3 is defeated by blue b5, red b5 is defeated by blue d3, and all other red moves are defeated by blue b4).

abcdefg12345671

Notice that the red stone at a6 is already connected south via the ladder escape at e5. Also, red threatens to connect north via a double threat at b3 and d3; each of these would connect to the northern edge via Template IIIa. The two templates overlap at d1, but blue d1 is defeated via the following sequence of forcing moves:

abcdefg12345672475361

Puzzle 2

A winning move is Red e3. This connects to the top edge via Template IIIa, and to the bottom edge via Template J5. The two templates overlap at one point d3, but if Blue plays there, Red can reply f3 to seal the connection up and down.

abcdefg12345671

Puzzle 3

The unique winning first move is Red c3! (e2 is defeated by e3, d3 is defeated by e1, e3 is defeated by e2, and b4 is defeated by d3).

abcdef1234561

The following seem like horizontal's (Blue's) best tries from the above position.

1. d2 e2 2. d5 c5 3. d4 b3 4. c4 a5
1. d3 b3 2. b5 e3
1. e1 d2 2. d1 d1 3. c4 b3 4. e3 a5 or 4. b5 e3
........ .... 2. c4 b3 3. c5 e3 4. e4 f3 5. e6 d5
1. d5 b3 2. d2 b2 3. c4 a5 4. a6 c5 5. b5 e3 6. d5 f5
........ .... ........ .... 3. b5 c5 4. c4 e3
........ .... ........ .... 3. b6 a6 4. b4 c5 5. c4 e3 6. e6 d4
1. c4 e3 2. e2 b3 3. d3 a5
1. b5 d4 2. d3 f2 3. f1 d2 4. c4 e2 5. e4 e3 6. c5 e5
........ .... 2. e1 d2 3. d1 f1 4. e2 f2...
1. b4 d2 2. d5 c5 3. c4 e3 4. d4 e5

Puzzle 4

abcdefg12345671

Red 1. c4 is the only way to prevent Blue from connecting immediately by b5, c3 or c4. Red threatens to connect c4 to the top and bottom edges with assistance from the ladder escapes at f2 and f5.

Blue 2. c5 is met by Red 3. a6, which connects to the bottom edge with assistance from the ladder escape at f5 and threatens to connect to c4 or climb to a4 and then connect to the top edge with assistance from the ladder escape at f2.

Blue may attempt a ladder escape fork by playing in the edge template between c4 and the top edge, but 2. c3 is met by 3. b4 and 2. c2 is met by 3. b3, which maintain the connection to the top edge and block Blue's ladder escape.

Eric Demer

Puzzle 1

The unique winning move is red a3. a2 is captured to the top edge, and Red threatens b4. e4 is a ladder escape, so b3 loses to a4 and b5 loses to b4. b4 capture-dominates a4 and a5. Thus Blue plays b4.

abcde1234512

Red responds with e2. This connects to the bottom edge by edge template IV2d, and connects to the top edge as shown.

abcde12345864753192

Uniqueness:

The shaded area is a virtual connection from c3, so Red must either play in it or play e2.

abcde12345

The rest of this paragraph uses edge template III2a extensively, and so we do not mention it each time it's used. If Red plays a5 or b4, then Blue plays b3, winning via d3 or e1. If Red plays a4, then Blue plays c4, connecting left via a3 or a5. a3 is Red's winning move. If Red plays b3, then Blue plays c2, connecting left via a3 or b4. If Red plays c2, then Blue plays c4, winning.

Red's only remaining try is e2. Blue responds with c4. After that, consider edge template III2a to the left edge.

abcde1234512

If Red intrudes there other than at *, then Blue responding at * captures those 6 cells. If Red intrudes at * before Red plays c2, then Blue responding at c2 still captures the template. Thus, until Red has played c2, Red has no useful way of even threatening to disconnect c3 from the left edge, so one gets

abcde123458647513323

At this point c3+c4 escapes the ladder from b2.


Puzzle 2

The unique winning move is blue d2.

abcde123451

This connects to the left edge via edge template IV2g, so Red must play either in there or e2. Against most intrusions in that template, Blue just responds with c3. Specifically, c3 almost makes this a second order template, since even if Red starts with two moves in it, the only way Red can stop Blue from reconnecting is if those moves are in the two cells marked "*":

bcd2345

Specifically, Red must have defended against b4. If Red did that with b4 or a5, then Blue reconnects with b3 or c1. Thus, Red needs a4. Red must have also defended against b3. If Red did that with b3 or a3, then Blue reconnects with c1. Thus, Red also needs b2.

Since Blue c3 connects to the right edge via edge template III2b, Red must play one of the shaded cells in the following diagram.

abcde123451

Blue responds to e2 with d4. Whether before or after that exchange, Blue responds to each of b2,a4 with b3. At least two of b2,a3,a4 would still be empty, so that allows Blue to climb, for example like this:

abcde12345712568439

Before the e2,d4 exchange, Blue responds to c3 with d4. After the e2,d4 exchange, Blue can respond to c3 with d3. In each case, Blue will have d2 and d4 captured to the right edge, so Red must defend against c1. If Red does so with b2, then b3 is an escape fork for the ladder from b5. If Red does so anywhere else, then a2 still escapes that ladder.

Thus, both before and immediately after the e2,d4 exchange, none of Red's intrusions into the edge template IV2g work, so Red must try e2 followed by d3. However, against that, Blue just plays b5, and ladders to a2.

abcde1234512435

Uniqueness:

Red's main threat is d3, bridging to edge template III2d. d2 is Blue's winning move. e2 and d3 lose to c3, since d5 escapes the ladder. d4 and c5 lose to b4, forming edge template IV2g.

If Blue plays c4, then Red plays b4. b4 will be captured to the bottom edge, so Blue must defend against c2. c3 loses to b3, since e1 escapes the ladder. The other four all lose to d3.

This leaves just b5. Red reponds with b4.

abcde1234521

That has a connection to the bottom edge, via a5 or c4, and threatens c2. If Blue plays c4, then Red plays a5, killing b5 and thereby reverting to the "Blue plays c4, then Red plays b4" case. If Blue intrudes in the other three cells of the connection from b4 to the bottom edge, then Red plays c4, re-establishing that connection and connecting to the top edge via edge template IV2a. Thus, Blue must defend against c2. c3 loses to b3, since e1 escapes the ladder. The other four all lose to d3, since that connects via d4 or a5.

Puzzle 3

The unique winning move is blue b2.

abcde123451

That captures a2 and a3, and threatens e1, so Red must play in c1,c2,e1. The b2-d1 bridge is bolstered at c1 (by Red's edge), so c1 is now worse than c2.

If Red plays c2, then Blue plays d2. That captures e1 and e2, so Red must respond with c1. Blue then plays b4, which connects left via e5 or b3, and connects right via edge template IV2e.

Thus Red plays e1. Blue responds with e2.

abcde12345213

Red must play in c1,c2,e1. As before, we discard c1. If Red plays c2, then Blue plays d2, killing e1 and thereby reverting to the "Red plays c2, then Blue plays d2" case. Thus Red plays d2. Blue responds with c4, connecting left via a5 or c3 and connecting right via e3 or d5.

Uniqueness:

I use it twice here, in already-dense prose, so I start with what I will call "the c4 ziggurat-defense":

If Blue plays in the e3 ziggurat other than at c4, then Red can respond at c4, after which Red can keep both c4 and e3 connected down inside the ziggurat: Either c4 is captured down, in which case e3 connects via one of {d3,d4,e4}, or Red can defend the bridge, in which case c4+e3 connects down via one of {b5,c5,e4}.

With that out of the way, suppose Blue plays anywhere other than the five cells marked "*" in the following diagram.

abcde12345

Red responds with b2, capturing b1 and c1. Blue gets one more move before it becomes Red's turn again, and Blue's two moves can't be Blue occupying both c4 and a5.

abcde123452

One of Blue's two moves must be in {a5,a3,b3}, and the other of Blue's two moves must defend against d2, since red d2 would connect down via edge template IV2i.

If that other move from Blue is not in the e3 ziggurat, then Red wins by laddering to e3: If Blue played a5 then Red plays b4, else Red defends the a4-b2 bridge.

If Blue played in the e3 ziggurat other than at c4, then Red uses the c4 ziggurat-defense, after which Red wins with d2 or the ladder along the bottom. Thus, one of Blue's two moves must be c4. This means Blue's other move can't be a5, so it must have been a3 or b3, to defend against red a5. In either case, Red plays b4, winning via either d2 or the other of a3,b3.

abcde12345265143

Thus, Blue must have played one of the five cells marked "*" in the following diagram.

abcde12345

b2 is Blue's winning move, and against the other four, Red plays d2.

If Blue has played b1 or c1, then we claim that the entire red-shaded region below is captured by Red:

abcde123452

To prove this, it is sufficient to show that Red has a strategy in the shaded region that keeps both a4 and d2 connected to the bottom edge. Because by the time the board is completely filled, if a4 and d2 are connected to the bottom edge, no minimal blue winning path can pass through the shaded area. Therefore all blue stones in that area will be dead.

To show that a4 and d2 are simultaneously connected down, consider any blue move in the region. If Blue plays b4, then Red responds with a5. In that case, d2 still connects down via edge template IV2i. Thus, Blue tries somewhere else in this region. Red responds at b4, and Blue gets one more move before it becomes Red's turn again.

If Blue's two moves were a5 and b5, then Red plays d4, connecting both d2 and b4 to the bottom with a trapezoid. Otherwise, Blue played at most one of a5,b5. If Blue played exactly one of those two, then Red plays the other, killing whichever of those two was Blue. In that case, Blue again gets one more move before it goes back to being Red's turn, so for showing this capture, we are left with the case where neither of Blue's was was in {a5,b5}. Since b4 is red, a5 and b5 are directly red-captured, so one of Blue's two moves must be c3, since otherwise Red plays there. The order in which Blue played Blue's two moves doesn't matter, so one can pretend Blue played c3 first. In that case, before Blue played Blue's other move, Red had a bridge to e3 and a connection from e3 due to the ladder escape at b4. Thus, Red can respond to restore the connection down from d2.

Due to this capture, the positions simplify to the following,

abcde123452

where the shading indicates that one of b1,c1 is blue and the other is empty.

Blue must play e1. After that, if c1 is empty, Red plays at c1 and is connected by a crescent, and if b1 is empty, Red plays at a2 and is connected by a different crescent and edge template II. This shows that both 1. b1 and 1. c1 are losing for Blue.

The remaining moves for Blue are a5 and c4. If Blue plays a5, then we claim that within the red-shaded region in the following diagram, Red can keep d2 connected down while ensuring that red b4 would connect down.

abcde1234521

The proof is similar to our proof of capture above. Specifically, before Blue plays there, d2 has a template down and red b4 would connect down since e3 escapes the ladder. If Blue plays b4, then red b4 can't happen and d2 still connects down, since b4 isn't in the template. If Blue plays c3, then Red plays d4, capturing d2 down and guaranteeing a ladder escape for red b4. The d2-e3 bridge is bolstered at e2, so e2 is worse than d3. If Red plays in the e3 ziggurat other than at c4, then Red uses the c4 ziggurat-defense, after which d2 connects down via c3 or e2, and red b4 would also connect down. If Blue plays c4, then Red plays d4. That captures d2 down, so red b4 would connect down via b5 or c3.

Given that, Red wins as follows:

abcde12345345261

Thus​ 1. a5​ loses, so Blue's only remaining try is ​1. c4.

abcde1234521

Red threatens

abcde12345421

and

abcde12345421

so Blue must play one of the cells shaded below.

abcde1234521

If Blue plays in {d5,d3,e2}, then Red plays b4, which captures a5 and b5, so Blue must defend against b2. Blue playing in {a3,b2,b1} loses to c2, Blue playing c1 loses to b3 - threatening e1 and a2 - and Blue playing b3 loses to b2, since that connects d2 to the top via e1 or c2.

If Blue plays e1 or c2, then Red plays

abcde12345426511811079

and then wins with whichever of e1,c2 Blue did not play.

If Blue plays c1, then Red plays b3 and defends that bridge. That connects to the top with a2 or e1 and to the bottom with a5 or d4.

If Blue plays b3, then Red plays b2. That captures b2 and d2 to the top, so Red wins with b4 or d4.

Lastly, if Blue plays a5, then Red wins as follows.

abcde1234556721081439

Puzzle 4

Uniqueness:

Blue's main threat is c2, bridging to edge template III2a.

abcde123452

If Red plays in {b1,b2,a2,a3}, then Blue plays b4, and wins with edge template IV2g. If Red plays a4, then Blue plays b2, and wins with d1 or c3.

If Red plays b3 or c2, then Blue plays b2, forcing d1.

abcde12345324

Blue continues with c3. This connects right via edge template III2d, and connects left with c2 or b3 or b4.

If Red plays d1, then Blue plays c3. That connects right with edge template III2d and connects left with a ziggurat.

There is only 1 remaining try for Red, and that is Red's winning move: d2

Showing that d2 wins for Red:

This part is quite similar to showing that d2 wins for Blue in puzzle 2.

abcde123451

The following region is a virtual connection:

abcde2345

d3 fails to c3, since e5 escapes the ladder, c3 and c4 fail to e3, forming edge template III2d, and everything else fails to c4, connecting down via one of b5,c5,d4.

Against most intrusions in that virtual connection, Red just responds with c3. Specifically, c3 almost makes this a second order connection, since even if Blue starts with two moves in it, the only way Blue can stop Red from reconnecting is if those moves are in the two cells marked "*":

abcde2345

Specifically, Blue must have defended against b4. Blue's other move must have been in {c4,d4,d3}, since otherwise Red plays d4 and connects with one of c5,d5,e4. d3 fails to c4, since e5 escapes the ladder, and c4 fails to e3, forming edge template III2d, so Blue's other move must be d4. This means a5 and b4 fail to c4, so Blue also needs b5.

Since red c3 connects to the top via d1 or b2, Blue must play one of the shaded cells in the following diagram.

abcde123451

Red responds to d1 with b2. Whether before or after that exchange, Red responds to each of b5,d4 with c4. c4 would connect down - via b5 or c5 or laddering to e5 - so that allows Red to climb, for example like this:

abcde12345238167954

Before the d1,b2 exchange, Red responds to c3 with b2. After the d1,b2 exchange, Red can respond to c3 with c2. In each case, Red will have b2 and d2 captured to the top edge, so Blue must defend against both e3 - forming edge template III2d - and the ladder escape fork at c4.

abcde23451

The overlap between those threats is {d3,c5}. Against d3, Red plays a4 and ladders to e5. Against c5, Red plays b5, followed by a4 or d3. (d3 connects with c4 or either of d4,e4).

Thus, both before and immediately after the d1,b2 exchange, none of Blue's intrusions into

abcde2345

work. Since b2 will be captured to a1, this means Blue must try d1 followed by c2. However, against that, Red just plays a4, and ladders to e5.

abcde1234523415

Puzzle 5

To find Red's winning move, let's use mustplay analysis to narrow down the possibilities. Blue has several threats, which are shown with their respective carriers:

Bridge to ziggurat:

abcde123451

b4 and double threat:

abcde123451

b4 and a different double threat:

abcde123451

Ladder and climbing from b2:

abcde1234554312

c4 with edge template III2b and ladder:

abcde1234553412

Red must play in the intersection of these carriers, i.e., at a4, a5, or b4.

Red a4 loses to Blue c3, with double threats towards both edges:

abcde1234521

Red a5 loses to Blue c2 as follows. Apart from attacking Blue's bridge, which Blue can simply defend, Red's moves 3 and 5 are forced, after which Blue wins by double threat:

abcde12345235461

This leaves b4 as the only possible move for Red.

Showing that b4 wins for Red:

abcde123451

If Blue plays to the upper-left of the short diagonal other than in {c2,b3}, then Red responds with c2 and defends the bridge. c2 connects to the top via d1 or c1 or b2, and connects to the bottom with a very short switchback.

abcde12345392541876

If Blue plays to the lower-right of the short diagonal other than at d4, then Red plays a5. This threatens c2, which would connect to the top via d1 or c1 or b2, so Blue must respond in {c2,c3,b3}. If Blue plays c2 or c3, then Red plays a3, winning with Edge template III2d. Thus Blue plays b3 instead. Red responds with d2, and a1 escapes that ladder.

abcde1234513

Blue must continue with c3, and what's left of this case is checking that Red can connect e2 down no matter which of the above shaded cells was Blue's first move. If that move was neither d3 nor e3, then Red bridges to d4, and connects down with c4 or c5 or d5. Otherwise, Red plays whichever of d3,e3 Blue didn't play. Since Red has a5 and b4, b5 is dead, so Red ladders to b4.

If Blue plays d4, then Red plays c4, capturing a5 and c5. This threatens c2, which would connect to the top via d1 or c1 or b2, so Blue must respond in {c2,c3,b3}. If Blue plays c2 or c3, then Red plays a3, winning with Edge template III2d. If Blue plays b3, then Red plays d2, bridging from c4 and laddering to a1.

This leaves the following tries for Blue.

abcde123451

c2 loses to a3, using Edge template III2d

abcde123452731654

and a switchback, as shown above.

If Blue plays b3, then Red plays d2, and a1 escapes that ladder. Towards the bottom, if Blue plays outside of {c4,c3,d3}, then Red can play c4 and defend the bridge from d2, and if Blue plays outside of {d4,d5,c5}, then Red can play d4 and defend the c5+d5 capture.

abcde12345321

In the former case, Red connects down with a5 or c5 or e4. In the latter case, Red connects down with e3 or d3 or c3, since c3 threatens c4 and a5. The sets {c4,c3,d3} and {d4,d5,c5} are disjoint, so Red gets at least one of those, and thereby connects down for a win.

If Blue plays c3, then Red plays d4, capturing e2 and b4 to the bottom. Blue must respond in {d2,c2,b3}, since otherwise Red plays c2, connecting down with d2 or b3 and connecting to the top with d1 or c1 or b2. If Blue plays d2 or c2, then Red plays a3, winning with Edge template III2d. If Blue plays b3, then Red plays d2, and wins by laddering to a1.

If Blue plays d2, then Red plays c3, connecting down with a5 or d4. Towards the top, blue c2 loses to a3, forming Edge template III2d, and Blue's other moves all lose to red c2, connecting with d1 or c1 or b2.

Blue's only remaining try is a5. Red responds to that with d4, capturing c5 and d5.

abcde12345132

Red's main threat is d4, laddering to a1.

abcde123455132

If Blue plays in {a2,b1,b2,c1,d1}, then Red plays c2. This connects to the top with d1 or c1 or b2, and connects down with a box.

If Blue plays c2, then Red plays d2. This connects down with a trapezoid, and connects to the top with d1 or a3, since a3 forms Edge template III2d.

If Blue plays d2, then Red plays c3. This has a bridge down, and connects to the top for the same reason as without the a5-b4 exchange.

The e2-d4 bridge is bolstered at e3 (by Blue's edge), so e3 is no better for Blue than d3.

Thus, the only remaining case is ​ ​ ​ 4. d3 ​ .

abcde1234541532

Against that, Red plays ​ ​ ​ 5. c4 ​ .

This threatens c2, which would connect to the top via d1 or c1 or b2, so Blue must respond in {c2,c3,b3}. If Blue plays c2 or c3, then Red plays a3, winning with Edge template III2d. Thus Blue plays b3 instead. Red responds with d2, connecting down via c3 or e3, and connecting to the top because a1 escapes the ladder.

Therefore ​ 1. b4 ​ does win for Red.

Puzzle 6

The unique winning move is c4. In the follow-up, Black must play d3 to get edge template IV2b::

abcdef12345625314

Puzzle 7

The unique winning move is c6:

abcdefg12345671

Indeed, now Blue is connected left by double threat at d4 or b6, and right by f6 or a ladder escape fork from f4. The uniqueness of the winning move is discussed in more detail in the article on the mustplay region.

Other authors

Puzzle 1

There are two main solutions. In the first line, Blue at (*) on move 7 or 9 is also winning.

abcdefghij12345678910213456897

In the second line, Blue has several winning moves starting move 9, but we show just one example.

abcdefghij12345678910435678910111221411315

Surprisingly, these are the only winning first moves for Blue. For example, 1. h8 is a losing move, but the refutation is subtle and depends on play in the lower-left obtuse corner:

abcdefghij12345678910119753121310864141521617181

However, Red's refutation fails when Blue plays 1. g8 instead, because after Red 12, Blue can instead play 13. d8! at (*), which threatens to connect to g8 (which wouldn't have been possible had Blue started with 1. h8).

Puzzle 2

Note that Red is connected upwards by Template J5. The only way to prevent Red from connecting downwards is to play in the cell marked (*).

abcdefg1234567

Perhaps surprisingly, (*) is a winning move, while any intrusion into the template on the first move is losing. If Red responds as expected at 2.c5, Blue's response is to intrude Red's upward connection at 3.b4. This leaves Blue in a strong position.

abcdefg1234567321

If Red instead plays 2.g4, Blue can respond with 3.d5, again leaving Blue in a strong position.

abcdefg1234567231
,

Other possible moves by Red also have a strong response, for example 2.c6 3.c4, or 2.d4 3.d5, or 2.d5 3.c4, or 2.e4 3.e5.

Puzzle 3

To simplify the analysis, it helps to note that because c9 connects to the left and a3 connects to the top, the left and top areas of the board are completely settled. Moreover, i2 captures j1 and j2 and kills h3, which in turns captures i3 and j3. Additionally, f6 and g5 are captured by Red. Therefore, the situation of the puzzle is equivalent to the following:

abcdefghij12345678910

Therefore, whatever Red can do, Red must do in the lower right corner. Here is how Red can win:

abcdefghij12345678910768945231

Puzzle 4

To simplify the analysis, it helps to note that Blue's g2 group is already connected to the right edge (see below), and Red's c6 group is already connected to the bottom edge. Moreover, Blue does not have any prospects for escaping a 2nd row ladder approaching the lower left from under c6. For these reasons, the position in the puzzle is equivalent to the following:

abcdefghij12345678910

Therefore, everything Blue can do must be done in the upper left corner. The winning move is c4:

abcdefghij123456789101

Blue 1. c4 threatens to connect left by b5 or c3 and right by d5, d4 or e3. If Red replies in the region a2-c2-c4-a6, other than at c3, to threaten c4's connection left, then Blue 3. c3 connects to the left edge, and to the right via e2 or d5. The only reply outside the region a2-c2-c4-a6 that prevents the group of 4 blue pieces connecting immediately to the left edge by d5, d4 or e3 is Red 2. d4. However, Red 2. d4 and 2. c3 can be answered by 3. e2.

To see why Blue's g2 group is connected right, Blue's main threats are 1. g5, connecting via Edge template IV1d and by the ladder escape fork 1. i1 2. j1 3. i3 4. i2 5. g4. Red can only meet both these threats by playing in overlap of these templates, in the marked cells.

abcdefghij12345678910

However these replies can be met by:

2. i3 3. i2 4. h2 5. g4 6. h3 7. h5

2. j3 3. i2 4. h2 5. g4 6. h3 7. h4 8. i3 9. i5

2. g4 3. i1 4. j1 5. i2 6. j2 7. i3 8. j3 9. i5 10. i4 11. h5 12. h4 13. f6

2. h4 then either 3. g4 threatening 5. i2 and 5. g6 - or simply 3. i2 4. h2 5. g4 6. h3 7. g6 - forming a crescent and connecting with the assistance of the second row ladder escape at i2

2. j2 3. h2 4. i2 (capture-dominates the alternatives i1 & j1) 5. h5 - a double ziggurat connection

[Note that although we used Edge template IV1d from g5 in the above explanation to minimise the overlap and the resulting case analysis, we don't need the whole template or the method of connection used for that. If however we use the smaller and simpler Edge template IV1a from g5, then the overlap with the ladder escape fork template is larger and we need to consider the additional replies h3, i2 and j1 (although j1 is capture-dominated by i2, so any winning variations against i2 also work against j1). Although 3. g5, connecting via Edge template IV1d, works against all these replies, there are simpler and quicker responses, e.g.: 2. h3 3. i4; 2. i2 3. h3 4. i3 5. h5 or 4.j3 5. i5; 2. j1 3. i3. So the analysis above only demonstrates that Blue is connected, rather than showing the smallest connection template or the quickest or simplest method of connection.]

Puzzle 5

Red's mustplay region consists of these 8 cells, because if Red plays anywhere else, Blue plays at d4 and wins immediately.

abcdef123456

The unique winning move is Red c4. Red then connects for example like this:

abcdef12345610861112975413132

Another move that looks plausible is Red d4, but it fails to this:

abcdef12345686475123

Puzzle 6

The unique winning move is b7. In the following line, Red's moves below (1, 3, 5, and 7) are the only moves that preserve the win. Note that moves 1 and 3 are minimaxing moves, while move 7 is a foiling move that blocks the ladder escape created from Blue 6.

abcdefghijklm123456789101112131324576

See Also

Back to puzzles page

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