A permutation of can be made to correspond to placing mutually nonattacking rooks on an chessboard if the permutation is place the rook on the rank and file Thinking of a chessboard as a matrix rank and file mean row and column A derangement is a permutation where no element stays in its original position; it corresponds to placing the rooks on the board with the added requirement that the squares on the main diagonal are forbidden Two other forbidden position problems are illustrated avoiding the main diagonal and the diagonal just above it and avoiding the main tridiagonal In this Demonstration a chessboard consists of white squares and black squares indicate forbidden positions