Theorem mt4

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

	Ref	Expression
Hypotheses	mt4.1	|- ph
	mt4.2	|- ( -. ps -> -. ph )
Assertion	mt4	|- ps

Proof

Step	Hyp	Ref	Expression
1		mt4.1	|- ph
2		mt4.2	|- ( -. ps -> -. ph )
3	2	con4i	|- ( ph -> ps )
4	1 3	ax-mp	|- ps