Every square in the close row for every player in the initial state has some
piece of that player.

A player moves by moving some piece of that player from some square to some
empty forward-adjacent square for that player of that square.
A player moves by moving some piece of the opponent of that player from some
forward-diagonal square for that player of some square to some cache square
for that opponent then moving the piece of that player from that square to
that forward-diagonal square.

A player wins when some square in the distant row for that player has some
piece of that player.

A player draws when no player wins and that player has no move.