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Theorem pm4.87 584
Description: Theorem *4.87 of [WhiteheadRussell] p. 122. (Contributed by NM, 3-Jan-2005.) (Proof shortened by Eric Schmidt, 26-Oct-2006.)
Assertion
Ref Expression
pm4.87

Proof of Theorem pm4.87
StepHypRef Expression
1 impexp 446 . . 3
2 bi2.04 361 . . 3
31, 2pm3.2i 455 . 2
4 impexp 446 . . 3
54bicomi 202 . 2
63, 5pm3.2i 455 1
Colors of variables: wff setvar class
Syntax hints:  ->wi 4  <->wb 184  /\wa 369
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-an 371
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