The object of the game is to remove all tiles from the field. Only two
matching tiles can be removed at a time. Two tiles can only be removed
if they can be connected with at most three connected lines. Lines can
be horizontal or vertical but not diagonal. Remember that lines may
cross the empty border. If you are stuck, you can use the Hint feature
to find two tiles which may be removed.

WWW: http://www.gnustep.it/enrico/gshisen/