Theorem mt2

Description: A rule similar to modus tollens. Inference associated with con2i . (Contributed by NM, 19-Aug-1993) (Proof shortened by Wolf Lammen, 10-Sep-2013)

	Ref	Expression
Hypotheses	mt2.1	|- ps
	mt2.2	|- ( ph -> -. ps )
Assertion	mt2	|- -. ph

Proof

Step	Hyp	Ref	Expression
1		mt2.1	|- ps
2		mt2.2	|- ( ph -> -. ps )
3	1	a1i	|- ( ph -> ps )
4	3 2	pm2.65i	|- -. ph