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Theorem oridm 495
Description: Idempotent law for disjunction. Theorem *4.25 of [WhiteheadRussell] p. 117. (The proof was shortened by Andrew Salmon, 16-Apr-2011.) (The proof was shortened by Wolf Lammen, 10-Mar-2013.)
Assertion
Ref Expression
oridm

Proof of Theorem oridm
StepHypRef Expression
1 pm1.2 494 . 2
2 pm2.07 383 . 2
31, 2impbii 178 1
Colors of variables: wff set class
Syntax hints:   wb 174   wo 356
This theorem is referenced by:  pm4.25 496  orordi 511  orordir 512  truortru 1276  falorfal 1279  unidm 2895  preqsn 3344  suceloni 4088  tz7.48lem 5772  msq0i 8377  prmdvdsexp 10854  pdivsq 18477  pm11.7 21971
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-3 7  ax-mp 8
This theorem depends on definitions:  df-bi 175  df-or 358
Copyright terms: Public domain