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describe the winning strategy

Source: ItaMO 2004, p4

March 4, 2012
functioncombinatorics proposedcombinatorics

Problem Statement

Antonio and Bernardo play the following game. They are given two piles of chips, one with mm and the other with nn chips. Antonio starts, and thereafter they make in turn one of the following moves: (i) take a chip from one pile; (ii) take a chip from each of the piles; (ii) remove a chip from one of the piles and put it onto the other. Who cannot make any more moves, loses. Decide, as a function of mm and nn if one of the players has a winning strategy, and in the case of the affirmative answer describe that strategy.