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Theorem con3 153
Description: Contraposition. Theorem *2.16 of [WhiteheadRussell] p. 103. This was the fourth axiom of Frege, specifically Proposition 28 of [Frege1879] p. 43. Its associated inference is con3i 154. (Contributed by NM, 29-Dec-1992.) (Proof shortened by Wolf Lammen, 13-Feb-2013.)
Assertion
Ref Expression
con3 ((𝜑𝜓) → (¬ 𝜓 → ¬ 𝜑))

Proof of Theorem con3
StepHypRef Expression
1 id 22 . 2 ((𝜑𝜓) → (𝜑𝜓))
21con3d 152 1 ((𝜑𝜓) → (¬ 𝜓 → ¬ 𝜑))
Colors of variables: wff setvar class
Syntax hints:  ¬ wn 3  wi 4
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8
This theorem is referenced by:  pm2.65  192  con34b  316  nic-ax  1676  nic-axALT  1677  axc10  2385  camestres  2669  baroco  2672  rexim  3088  falseral0  4520  dfon2lem9  34763  hbntg  34777  naim1  35274  naim2  35275  lukshef-ax2  35300  bj-eximALT  35518  bj-axc10v  35671  ax12indn  37813  cvrexchlem  38290  cvratlem  38292  axfrege28  42580  vk15.4j  43289  tratrb  43297  hbntal  43314  tratrbVD  43622  con5VD  43661  vk15.4jVD  43675  nrhmzr  46647
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