collectable_object(landfill, 0, 0).
collectable_object(landfill, 1, 0).
collectable_object(landfill, 2, 0).
collectable_object(house, 8, 6).
collectable_object(house, 6, 8).
collectable_object(house, 2, 6).
collectable_object(house, 8, 8).
collectable_object(house, 9, 2).
collectable_object(house, 5, 3).