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Theorem dfor2 411
Description: Logical 'or' expressed in terms of implication only. Theorem *5.25 of [WhiteheadRussell] p. 124. (Contributed by NM, 12-Aug-2004.) (Proof shortened by Wolf Lammen, 20-Oct-2012.)
Assertion
Ref Expression
dfor2

Proof of Theorem dfor2
StepHypRef Expression
1 pm2.62 409 . 2
2 pm2.68 410 . 2
31, 2impbii 188 1
Colors of variables: wff setvar class
Syntax hints:  ->wi 4  <->wb 184  \/wo 368
This theorem is referenced by:  imimorb  877
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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