As the name implies, you pair up two moves and keep doing it until you pair up everything. The strategy is if your opponent makes one of the moves in a certain pair, you proceed with the other move in that pair (so you need to make sure the pairing is done right so the move you want to make in that pair is available). And of course, you want to pair to prevent the opponent from winning, which hard part.

Example: On a lattice, green and red take turns connecting horizontally or vertically adjacent dots with an edge of his color and the first to form a loop of his color wins. 1st player (green) has an advantage, but is it enough to guarantee a win? If not, how can red force a draw?

[To form a loop, you have to turn and one of the turn will look like an L. Pick a possible move and pair it with the move that combines to form an L. Repeat for the remaining moves. Since all L have two colors, there can’t be a loop with one color].

Exercise: On a checker board, green and red take turns placing a checker of his color on the board. To win you need to have a 2 by 2 square of your color. What should red do?

[Pictorially, it’s a brick house with each pair being a brick. Pick a row, pair the first two from the right and keep doing it as you move left. Green can’t bunch up at the first two, but can bunch up in the second and third. So for the next row above and below, pair up the second and third, and repeat as you move left.]