This is a famous ending named "双炮禁双炮". As I said before, it's equivalent to a game of removing matches (or stones) from several stackes. The rule is that two players take turns removing any positive number of matches from a single stack and whoever gets the last match wins. To win this game, represent the number of matches of each stack in binary format, and try to maintain even number of one's in every digit. To be specific, as in this game, there are 4 and 6 spots between 2 cannons and 2 spot between the pawns. Our objective is to have the last move so that the four cannons are touches, and have 1 spot left between the pawns. So we can think of 3 stackes of matches with 1, 4, and 6 matches, respectively. Represent them as binary number, we have 1, 100, and 110. So the first move is reduce 6 to 5, and make it 101. Now we have 1, 100, and 101. Note here we have even number of 1's in every digit. www.ddhw.com
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