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Theorem con1b 346
Description: Contraposition. Bidirectional version of con1 141. (Contributed by NM, 3-Jan-1993.)
Assertion
Ref Expression
con1b ((¬ 𝜑𝜓) ↔ (¬ 𝜓𝜑))

Proof of Theorem con1b
StepHypRef Expression
1 con1 141 . 2 ((¬ 𝜑𝜓) → (¬ 𝜓𝜑))
2 con1 141 . 2 ((¬ 𝜓𝜑) → (¬ 𝜑𝜓))
31, 2impbii 197 1 ((¬ 𝜑𝜓) ↔ (¬ 𝜓𝜑))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4  wb 194
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 195
This theorem is referenced by:  eximal  1697  r19.23v  3000  pwssun  4930  ist1-2  20899  cmpfi  20959  dchrelbas2  24675
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