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Theorem pm4.53r 804
Description: One direction of theorem *4.53 of [WhiteheadRussell] p. 120. The converse also holds in classical logic. (Contributed by Jim Kingdon, 27-Jul-2018.)
Assertion
Ref Expression
pm4.53r  |-  ( ( -.  ph  \/  ps )  ->  -.  ( ph  /\ 
-.  ps ) )

Proof of Theorem pm4.53r
StepHypRef Expression
1 pm4.52im 803 . 2  |-  ( (
ph  /\  -.  ps )  ->  -.  ( -.  ph  \/  ps ) )
21con2i 557 1  |-  ( ( -.  ph  \/  ps )  ->  -.  ( ph  /\ 
-.  ps ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4    /\ wa 97    \/ wo 629
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545  ax-io 630
This theorem depends on definitions:  df-bi 110
This theorem is referenced by:  undif3ss  3198
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