Theorem necon4adOLD 2678

Description: Obsolete proof of necon4ad 2677 as of 23-Nov-2019. (Contributed by NM, 2-Apr-2007.) (Proof shortened by Andrew Salmon, 25-May-2011.) (Proof modification is discouraged.) (New usage is discouraged.)

Hypothesis

Ref	Expression
necon4ad.1

Assertion

Ref	Expression
necon4adOLD

Proof of Theorem necon4adOLD

Step	Hyp	Ref	Expression
1		necon4ad.1	. . 3
2	1	con2d 115	. 2
3		nne 2658	. 2
4	2, 3	syl6ib 226	1

Syntax hints:  -.wn 3  ->wi 4  =wceq 1395  =/=wne 2652

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

This theorem depends on definitions:  df-bi 185  df-ne 2654