Theorem mt4

Description: The rule of modus tollens. Inference associated with con4i . (Contributed by Wolf Lammen, 12-May-2013)

	Ref	Expression
Hypotheses	mt4.1	$$⊢\phi$$
	mt4.2	$$⊢\neg \psi \to \neg \phi$$
Assertion	mt4	$$⊢\psi$$

Proof

Step	Hyp	Ref	Expression
1		mt4.1	$$⊢\phi$$
2		mt4.2	$$⊢\neg \psi \to \neg \phi$$
3	2	con4i	$$⊢\phi \to \psi$$
4	1 3	ax-mp	$$⊢\psi$$