checkerboard = ap ap s ap ap b s ap ap c ap ap b c ap ap b ap c ap c ap ap s ap ap b s ap ap b ap b ap ap s i i lt eq ap ap s mul i nil ap ap s ap ap b s ap ap b ap b cons ap ap s ap ap b s ap ap b ap b cons ap c div ap c ap ap s ap ap b b ap ap c ap ap b b add neg ap ap b ap s mul div ap ap c ap ap b b checkerboard ap ap c add 2
