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Found problems: 1

2019 Canada National Olympiad, 3
Tags: combinatorics , tilings , checkerboard , combinatorics solved , grids , Bijections , induction
You have a $2m$ by $2n$ grid of squares coloured in the same way as a standard checkerboard. Find the total number of ways to place $mn$ counters on white squares so that each square contains at most one counter and no two counters are in diagonally adjacent white squares.