  We prove computational intractability of variants of checkers: (1) deciding
whether there is a move that forces the other player to win in one move is
NP-complete; (2) checkers where players must always be able to jump on their
turn is PSPACE-complete; and (3) cooperative versions of (1) and (2) are
NP-complete. We also give cooperative checkers puzzles whose solutions are the
letters of the alphabet.
