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Metamath Proof Explorer

Theorem pm5.41

Description: Theorem *5.41 of WhiteheadRussell p. 125. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 12-Oct-2012)

Ref Expression
Assertion pm5.41 
|- ( ( ( ph -> ps ) -> ( ph -> ch ) ) <-> ( ph -> ( ps -> ch ) ) )

Proof

Step Hyp Ref Expression
1 imdi 
 |-  ( ( ph -> ( ps -> ch ) ) <-> ( ( ph -> ps ) -> ( ph -> ch ) ) )
2 1 bicomi 
 |-  ( ( ( ph -> ps ) -> ( ph -> ch ) ) <-> ( ph -> ( ps -> ch ) ) )