Theorem con4iOLD 145

Description: Obsolete proof of con4i 113 as of 15-Jul-2021. This shorter proof has been reverted to its original to avoid a dependency on ax-1 6 and ax-2 7. (Contributed by NM, 29-Dec-1992.) (Proof shortened by Wolf Lammen, 21-Jun-2013.) (Proof modification is discouraged.) (New usage is discouraged.)

Hypothesis

Ref	Expression
con4iOLD.1	|- ( -. ph -> -. ps )

Assertion

Ref	Expression
con4iOLD	|- ( ps -> ph )

Proof of Theorem con4iOLD

Step	Hyp	Ref	Expression
1		notnot 136	. 2 |- ( ps -> -. -. ps )
2		con4iOLD.1	. 2 |- ( -. ph -> -. ps )
3	1, 2	nsyl2 142	1 |- ( ps -> ph )

Syntax hints:   -. wn 3   -> wi 4

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem is referenced by: (None)