p cnf 20 12 q 0 q 20 0 q 10 0 q 19 0 q 9 0 q 18 0 q 8 0 q 17 0 q 7 0 q 16 0 q 6 0 q 15 0 q 5 0 q 14 0 q 4 0 q 13 0 q 3 0 q 12 0 q 2 0 q 11 0 q 1 0 -10 0 10 19 -9 -18 -8 0 9 18 -8 -17 -7 0 8 17 -7 -16 -6 0 7 16 -6 -15 -5 0 6 15 -5 -14 -4 0 5 14 -4 -13 -3 0 4 13 -3 -12 -2 0 3 12 -2 -11 -1 0 2 1 0 2 -1 0 -2 1 0