Tom's move
Contents
Introduction
Tom's move is a trick that enables a player to make a connection from a 2nd-and-4th row parallel ladder. It can also be used to break through a 2nd row ladder using a single stone on the 4th row, or to connect a single stone on the 4th row to the edge. Its name originates from Tom Ace (player Tom239), who devised it during a game against dj11, on 15 December 2002 on Playsite. This was not its first use ever, just how it came to be known among Hex players on Playsite.
Description
Suppose Red has a 2nd-and-4th row parallel ladder and the amount of space shown here:
Then Red can connect by playing at "*", the so-called "Tom's move".
Usage examples
Connecting a 2nd row ladder using an isolated stone on the 4th row
Red to move and win:
The solution is to push the ladder to 3 and then play Tom's move:
A single stone on the 4th row is connected
Consider a single stone on the 4th row, with the amount of space shown:
Then Red can connect as follows:
Red squeezes through the bottleneck at 2, starts a 2nd row ladder at 4, then plays Tom's move at 6. Note that all of Blue's moves are forced; if Blue plays differently, Red connects outright.
In a game
Red to move:
Red's d4 group is already connected to the top edge by edge template IV1-a. To connect to the bottom, Red plays as follows:
Now Red is connected by Tom's move. Note that d8 is already connected to Red's group by double threat at c8 and d9.
Why Tom's move is connected
Let us compute Blue's mustplay region. Red has several main threats:
Blue's mustplay region consists of the intersection of the carriers of these threats, which means that Blue's only hope is to play at 1.
Red responds like this:
The group containing 4 is now connected to the bottom via edge template III2-b, and to Red's main group by double threat at the cells marked "*". Note that 2 and 3 do not actually need to be played; these moves have been included for clarity.
