Theorem bi2.04 248

Description: Logical equivalence of commuted antecedents. Part of Theorem *4.87 of [WhiteheadRussell] p. 122. (Contributed by NM, 5-Aug-1993.)

Assertion

Ref	Expression
bi2.04	|- ( ( ph -> ( ps -> ch ) ) <-> ( ps -> ( ph -> ch ) ) )

Proof of Theorem bi2.04

Step	Hyp	Ref	Expression
1		pm2.04 82	. 2 |- ( ( ph -> ( ps -> ch ) ) -> ( ps -> ( ph -> ch ) ) )
2		pm2.04 82	. 2 |- ( ( ps -> ( ph -> ch ) ) -> ( ph -> ( ps -> ch ) ) )
3	1, 2	impbii 126	1 |- ( ( ph -> ( ps -> ch ) ) <-> ( ps -> ( ph -> ch ) ) )

Syntax hints:   -> wi 4   <-> wb 105

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia2 107  ax-ia3 108

This theorem depends on definitions:  df-bi 117

This theorem is referenced by:  imim21b  253  pm4.87  557  imimorbdc  901  sbcom2v  2036  mor  2120  r19.21t  2605  reu8  2999  ra5  3118  unissb  3918  reusv3  4551  zfregfr  4666  tfi  4674  fun11  5388  prime  9546  raluz2  9774  isprm3  12640  isprm4  12641  bj-inf2vnlem2  16334