Theorem con3 154

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 155. (Contributed by NM, 29-Dec-1992.) (Proof shortened by Wolf Lammen, 13-Feb-2013.)

Assertion

Ref	Expression
con3	⊢ ((𝜑 → 𝜓) → (¬ 𝜓 → ¬ 𝜑))

Proof of Theorem con3

Step	Hyp	Ref	Expression
1		id 23	. 2 ⊢ ((𝜑 → 𝜓) → (𝜑 → 𝜓))
2	1	con3d 153	1 ⊢ ((𝜑 → 𝜓) → (¬ 𝜓 → ¬ 𝜑))

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  195  con34b  319  nic-ax  1703  nic-axALT  1704  axc10  2417  camestres  2700  baroco  2703  rexim  3106  falseral0OLD  4477  nrhmzr  20623  cbvex1v  35443  antnestlaw2  36165  dfon2lem9  36262  hbntg  36276  naim1  36881  naim2  36882  lukshef-ax2  36907  bj-exim  37213  bj-axc10v  37409  ax12indn  39698  cvrexchlem  40174  cvratlem  40176  axfrege28  44538  vk15.4j  45220  tratrb  45228  hbntal  45245  tratrbVD  45552  con5VD  45591  vk15.4jVD  45605