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Theorem pm4.81 415
Description: Theorem *4.81 of [WhiteheadRussell] p. 122.
Assertion
Ref Expression
pm4.81 |- ((-. ph -> ph) <-> ph)

Proof of Theorem pm4.81
StepHypRef Expression
1 pm2.18 112 . 2 |- ((-. ph -> ph) -> ph)
2 pm2.24 111 . 2 |- (ph -> (-. ph -> ph))
31, 2impbii 213 1 |- ((-. ph -> ph) <-> ph)
Colors of variables: wff set class
Syntax hints:  -. wn 2   -> wi 3   <-> wb 209
This theorem is referenced by:  oridmOLD 583
This theorem was proved from axioms:  ax-1 4  ax-2 5  ax-3 6  ax-mp 7
This theorem depends on definitions:  df-bi 210
Copyright terms: Public domain