Theorem pm2.61ian

Description: Elimination of an antecedent. (Contributed by NM, 1-Jan-2005)

	Ref	Expression
Hypotheses	pm2.61ian.1	|- ( ( ph /\ ps ) -> ch )
	pm2.61ian.2	|- ( ( -. ph /\ ps ) -> ch )
Assertion	pm2.61ian	|- ( ps -> ch )

Proof

Step	Hyp	Ref	Expression
1		pm2.61ian.1	|- ( ( ph /\ ps ) -> ch )
2		pm2.61ian.2	|- ( ( -. ph /\ ps ) -> ch )
3	1	ex	|- ( ph -> ( ps -> ch ) )
4	2	ex	|- ( -. ph -> ( ps -> ch ) )
5	3 4	pm2.61i	|- ( ps -> ch )