The squares of an
checkerboard are alternately colored black and red. It has been shown that for every
pair
of positive integers, it is possible to place coins on some of the squares of the
checkerboard (at most one coin per square) in such a way that for every two squares
of the same color the numbers of coins on neighboring squares are of the same
parity, while for every two squares of different colors the numbers of coins on
neighboring squares are of opposite parity. All solutions to this problem have
been what is referred to as trivial solutions, namely, for either black or red,
no coins are placed on any square of that color. A nontrivial solution then
requires at least one coin to be placed on a square of each color. For some pairs
of
positive integers, however, nontrivial solutions do not exist. All pairs
of
positive integers are determined for which there is a nontrivial solution.