Theorem excomOLD 1859

Description: Obsolete proof of excom 1741 as of 8-Jan-2018. (Contributed by NM, 5-Aug-1993.) (Proof modification is discouraged.) (New usage is discouraged.)

Assertion

Ref	Expression
excomOLD	|- (E.xE.yph <-> E.yE.xph)

Proof of Theorem excomOLD

Step	Hyp	Ref	Expression
1		excomim 1742	. 2 |- (E.xE.yph -> E.yE.xph)
2		excomim 1742	. 2 |- (E.yE.xph -> E.xE.yph)
3	1, 2	impbii 180	1 |- (E.xE.yph <-> E.yE.xph)

Syntax hints:   <-> wb 176  E.wex 1541

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1546  ax-5 1557  ax-7 1734

This theorem depends on definitions:  df-bi 177  df-ex 1542

This theorem is referenced by: (None)