  For any two squares A and B of an m x n checkerboard, we determine whether it
is possible to move a checker through a route that starts at A, ends at B, and
visits each square of the board exactly once. Each step of the route moves to
an adjacent square, either to the east or to the north, and may step off the
edge of the board in a manner corresponding to the usual construction of a
projective plane by applying a twist when gluing opposite sides of a rectangle.
This generalizes work of M.H.Forbush et al. for the special case where m = n.
