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Theorem pm3.1 670
Description: Theorem *3.1 of [WhiteheadRussell] p. 111. The converse holds for decidable propositions, as seen at anordc 862. (Contributed by NM, 3-Jan-2005.) (Revised by Mario Carneiro, 31-Jan-2015.)
Assertion
Ref Expression
pm3.1 ((φ ψ) → ¬ (¬ φ ¬ ψ))

Proof of Theorem pm3.1
StepHypRef Expression
1 pm3.14 669 . 2 ((¬ φ ¬ ψ) → ¬ (φ ψ))
21con2i 557 1 ((φ ψ) → ¬ (¬ φ ¬ ψ))
Colors of variables: wff set class
Syntax hints:  ¬ wn 3  wi 4   wa 97   wo 628
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545  ax-io 629
This theorem depends on definitions:  df-bi 110
This theorem is referenced by:  inssun  3171
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