User:Selinger
Proposed article: Hygiene
Hygiene refers to basic preventative measures that decrease the likelihood of bad things happening in the future. For example, hand washing decreases the likelihood of getting sick. Hygiene is not a reaction to a specific imminent threat, but a set of general-purpose good practices. In Hex, if a player can make a move that carries no cost or risk, but decreases the chance of something bad happening in the future, it is good hygiene to make the move.
Examples
Acute corner example
Consider the following situation, where Red has just played 1 to connect her group to the bottom edge.
Blue would like to play elsewhere on the board. However, this would leave Red with a 2nd row ladder escape along the bottom edge. While this ladder escape may not look immediately threatening to Blue, it would be bad hygiene to just leave it unattended. Instead, Blue first plays 2, which forces Red to reconnect, say at 3.
Now Blue has taken away Red's ladder escape and is free to move elsewhere. In fact, Blue also gained a small amount of territory.
To illustrate that this can make a difference, consider the following contrived position, with Blue to move. In this situation, "a" is winning, but "b" and all other moves are losing.
Obtuse corner example
Red has just played 1, threatening to connect to the bottom edge. Blue responded at 2. The result will be a 2nd row ladder along the bottom edge.
Let's assume that the ladder is threatening to Blue, i.e., either Red can escape the ladder outright, or gain some other benefit (such as climbing) from playing the ladder. Red could either start the ladder right away, or first play elsewhere. In either case, it is good hygiene to first play 3 and 4:
Note that 3 is immediately forcing: if Blue does not respond, Red connects to the edge. On the other hand, if Red first plays the ladder along the right edge and connects, 3 is no longer forcing. In addition to gaining a bit of territory for Red, moving at 3 also removes any possibility that 2 could help with a blue ladder arriving along the left edge.
To illustrate that this can make a difference, consider the following contrived position, with Red to move. In this situation, "a" is winning, but "b" and all other moves are losing.
