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Metamath Proof Explorer

Theorem pm2.73

Description: Theorem *2.73 of WhiteheadRussell p. 108. (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.73 
|- ( ( ph -> ps ) -> ( ( ( ph \/ ps ) \/ ch ) -> ( ps \/ ch ) ) )

Proof

Step Hyp Ref Expression
1 pm2.621 
 |-  ( ( ph -> ps ) -> ( ( ph \/ ps ) -> ps ) )
2 1 orim1d 
 |-  ( ( ph -> ps ) -> ( ( ( ph \/ ps ) \/ ch ) -> ( ps \/ ch ) ) )