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Theorem pm4.81ALT 30958
Description: Alternate proof of pm4.81 367. (Contributed by BJ, 30-Mar-2020.) (Proof modification is discouraged.) (New usage is discouraged.)
Assertion
Ref Expression
pm4.81ALT  |-  ( ( -.  ph  ->  ph )  <->  ph )

Proof of Theorem pm4.81ALT
StepHypRef Expression
1 pm2.18 113 . 2  |-  ( ( -.  ph  ->  ph )  ->  ph )
2 ax-1 6 . 2  |-  ( ph  ->  ( -.  ph  ->  ph ) )
31, 2impbii 190 1  |-  ( ( -.  ph  ->  ph )  <->  ph )
Colors of variables: wff setvar class
Syntax hints:   -. wn 3    -> wi 4    <-> wb 187
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem depends on definitions:  df-bi 188
This theorem is referenced by: (None)
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