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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  1279  falorfal  1282  unidm  2955  preqsn  3404  suceloni  4164  tz7.48lem  5877  msq0i  8534  prmdvdsexp  11022  pdivsq  18783  pm11.7  22269
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