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Theorem con2b 592
Description: Contraposition. Bidirectional version of con2 571. (Contributed by NM, 5-Aug-1993.)
Assertion
Ref Expression
con2b ((φ → ¬ ψ) ↔ (ψ → ¬ φ))

Proof of Theorem con2b
StepHypRef Expression
1 con2 571 . 2 ((φ → ¬ ψ) → (ψ → ¬ φ))
2 con2 571 . 2 ((ψ → ¬ φ) → (φ → ¬ ψ))
31, 2impbii 117 1 ((φ → ¬ ψ) ↔ (ψ → ¬ φ))
Colors of variables: wff set class
Syntax hints:  ¬ wn 3  wi 4  wb 98
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia2 100  ax-ia3 101  ax-in1 544  ax-in2 545
This theorem depends on definitions:  df-bi 110
This theorem is referenced by:  mt2bi  608  pm4.15  788  ssconb  3070  disjsn  3423
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