for (int c0 = -9; c0 <= 9; c0 += 1)
for (int c1 = max(1, -c0 + 1); c1 <= min(10, -c0 + 10); c1 += 1)
s0(c0, c1);
for (int c0 = -9; c0 <= 9; c0 += 1)
for (int c1 = max(1, -c0 + 1); c1 <= min(10, -c0 + 10); c1 += 1)
s0(c0, c1);