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 ) ) )

This proof depends on syntax axioms:   -> wi 4   <-> wb 105

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia2 107  ax-ia3 108

This proof depends on definitions:  df-bi 117

This theorem is used by:  imim21b  253  pm4.87  563  imimorbdc  908  sbcom2v  2045  mor  2129  r19.21t  2625  reu8  3022  ra5  3141  unissb  3965  reusv3  4608  zfregfr  4723  tfi  4731  fun11  5451  prime  9756  raluz2  9995  isprm3  12921  isprm4  12922  bj-inf2vnlem2  17202