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Metamath Proof Explorer

Theorem pm2.521

Description: Theorem *2.521 of WhiteheadRussell p. 107. Instance of pm2.521g and of pm2.521g2 . (Contributed by NM, 3-Jan-2005)

Ref Expression
Assertion pm2.521 
|- ( -. ( ph -> ps ) -> ( ps -> ph ) )

Proof

Step Hyp Ref Expression
1 pm2.521g 
 |-  ( -. ( ph -> ps ) -> ( ps -> ph ) )