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Theorem con1b 348
Description: Contraposition. Bidirectional version of con1 143. (Contributed by NM, 3-Jan-1993.)
Assertion
Ref Expression
con1b ((¬ 𝜑𝜓) ↔ (¬ 𝜓𝜑))

Proof of Theorem con1b
StepHypRef Expression
1 con1 143 . 2 ((¬ 𝜑𝜓) → (¬ 𝜓𝜑))
2 con1 143 . 2 ((¬ 𝜓𝜑) → (¬ 𝜑𝜓))
31, 2impbii 199 1 ((¬ 𝜑𝜓) ↔ (¬ 𝜓𝜑))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wb 196
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 197
This theorem is referenced by:  eximal  1705  r19.23v  3019  pwssun  5010  ist1-2  21132  cmpfi  21192  dchrelbas2  24943
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