Theorem pm2.65da

Description: Deduction for proof by contradiction. (Contributed by NM, 12-Jun-2014)

	Ref	Expression
Hypotheses	pm2.65da.1	|- ( ( ph /\ ps ) -> ch )
	pm2.65da.2	|- ( ( ph /\ ps ) -> -. ch )
Assertion	pm2.65da	|- ( ph -> -. ps )

Proof

Step	Hyp	Ref	Expression
1		pm2.65da.1	|- ( ( ph /\ ps ) -> ch )
2		pm2.65da.2	|- ( ( ph /\ ps ) -> -. ch )
3	1	ex	|- ( ph -> ( ps -> ch ) )
4	2	ex	|- ( ph -> ( ps -> -. ch ) )
5	3 4	pm2.65d	|- ( ph -> -. ps )