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Theorem pm5.55 892
Description: Theorem *5.55 of [WhiteheadRussell] p. 125. (Contributed by NM, 3-Jan-2005.) (Proof shortened by Wolf Lammen, 20-Jan-2013.)
Assertion
Ref Expression
pm5.55

Proof of Theorem pm5.55
StepHypRef Expression
1 biort 891 . . . . 5
21bicomd 201 . . . 4
3 biorf 405 . . . . 5
43bicomd 201 . . . 4
52, 4nsyl4 142 . . 3
65con1i 129 . 2
76orri 376 1
Colors of variables: wff setvar class
Syntax hints:  -.wn 3  <->wb 184  \/wo 368
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 185  df-or 370
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