you cannot cover all squares with dominos
... that if you remove two opposite corners of a chessboard, you cannot cover all squares with dominos?
... that if you remove two opposite corners of a chessboard, <b id="mwA0s"><a href="./Mutilated_chessboard_problem" id="mwA0w" rel="mw:WikiLink" title="Mutilated chessboard problem">you cannot cover all squares with dominos</a></b>?