IMO Shortlist 2012 problem C5
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Avg: 8,0 The columns and the row of a square board are numbered . Every square with is colored asparagus, byzantium or citrine according as the modulo remainder of is or respectively. One token colored asparagus, byzantium or citrine is placed on each square, so that there are tokens of each color.
Suppose that on can permute the tokens so that each token is moved to a distance of at most from its original position, each asparagus token replaces a byzantium token, each byzantium token replaces a citirine token, and each citrine token replaces an aspargus token. Prove that it is possible to permute the tokens so that each token is moved to a distance of at most from its original position, and each square contains a token with the same color as the square.
Suppose that on can permute the tokens so that each token is moved to a distance of at most from its original position, each asparagus token replaces a byzantium token, each byzantium token replaces a citirine token, and each citrine token replaces an aspargus token. Prove that it is possible to permute the tokens so that each token is moved to a distance of at most from its original position, and each square contains a token with the same color as the square.
Izvor: Međunarodna matematička olimpijada, shortlist 2012