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Theorem orabs 828
Description: Absorption of redundant internal disjunct. Compare Theorem *4.45 of [WhiteheadRussell] p. 119. (Contributed by NM, 5-Aug-1993.) (Proof shortened by Wolf Lammen, 28-Feb-2014.)
Assertion
Ref Expression
orabs (φ ↔ ((φ ψ) φ))

Proof of Theorem orabs
StepHypRef Expression
1 orc 374 . 2 (φ → (φ ψ))
21pm4.71ri 614 1 (φ ↔ ((φ ψ) φ))
Colors of variables: wff setvar class
Syntax hints:  wb 176   wo 357   wa 358
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 177  df-or 359  df-an 360
This theorem is referenced by: (None)
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