Theorem nsyld

Description: A negated syllogism deduction. (Contributed by NM, 9-Apr-2005)

	Ref	Expression
Hypotheses	nsyld.1	|- ( ph -> ( ps -> -. ch ) )
	nsyld.2	|- ( ph -> ( ta -> ch ) )
Assertion	nsyld	|- ( ph -> ( ps -> -. ta ) )

Proof

Step	Hyp	Ref	Expression
1		nsyld.1	|- ( ph -> ( ps -> -. ch ) )
2		nsyld.2	|- ( ph -> ( ta -> ch ) )
3	2	con3d	|- ( ph -> ( -. ch -> -. ta ) )
4	1 3	syld	|- ( ph -> ( ps -> -. ta ) )