Home work 2. Due Feb 27th.
Consider covering slightly mutilated 6 by 6 checker boards with
tiles of size 1 by 2. Show that if the board is missing square
(1,6) and (1,5) then there is a covering; and if the board is
missing square (1,6) and (6,1) then there is no covering.
Warning: Some version of smodels have a bug and don't seem to
correctly handle atoms in the head with terms such as X+1,