Theorem pm2.65ni

Description: Inference rule for proof by contradiction. (Contributed by Glauco Siliprandi, 5-Apr-2020)

	Ref	Expression
Hypotheses	pm2.65ni.1	|- ( -. ph -> ps )
	pm2.65ni.2	|- ( -. ph -> -. ps )
Assertion	pm2.65ni	|- ph

Proof

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