Xavier and Yolanda are playing a game starting with some coins arranged in piles. Xavier always goes first, and the two players take turns removing one or more coins from any one pile. The player who takes the last coin wins. If there are two piles of coins with 3 coins in each pile, show that Yolanda can guarantee that she always wins the game.
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Source: CEMC, University of Waterloo,
licensed CC-BY-NC-4.0.
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