 \({\sim}(A \supset B)\) is equivalent to \(A \amp{\sim}B\). Intuitively, you may safely say, of an unseen geometric figure, “It’s not the case that if it’s a pentagon, it has six sides”. But by Hook’s lights, you may well be wrong; for it may not be a pentagon, and in that case it is true that if it’s a pentagon, it has six sides. 