◻Play Dots and Boxes

Dots and Boxes was published by the French mathematician Édouard Lucas in 1889, and it looks like a children's game right up to the point where it stops being one. The opening is nearly meaningless and the endgame is a piece of combinatorial theory.

Everything turns on chains. Once the safe moves run out, the board is a set of chains of boxes, and whoever is forced to open one gives it away. The player who understands this is not trying to take boxes — they are trying to control the parity of how many safe moves remain, so their opponent runs out first.

The advanced technique is the double-cross: rather than take every box in a chain you have been given, you leave the last two, which forces your opponent to open the next chain instead of you. Giving away two boxes to gain a chain of six is the move that decides most serious games.

The computer here takes any box it can and otherwise avoids handing you one, which is enough to punish careless play. It does not count chain parity, so a player who does can beat it consistently.