 Commutativity of refutation  Refutation, on the contrary, is commutative, but not contrapositive. That is, it holds that \(e\) refutes \(h\) \((e\vDash \neg h)\) if and only if \(h\) refutes \(e\) \((h\vDash \neg e)\), while it does not hold that \(e\) refutes \(h\) if and only if \(\neg h\) refutes \(\neg e\) \((\neg h \vDash \neg\neg e).\)