Theorem orel2 728

Description: Elimination of disjunction by denial of a disjunct. Theorem *2.56 of [WhiteheadRussell] p. 107. (Contributed by NM, 12-Aug-1994.) (Proof shortened by Wolf Lammen, 5-Apr-2013.)

Assertion

Ref	Expression
orel2	⊢ (¬ 𝜑 → ((𝜓 ∨ 𝜑) → 𝜓))

Proof of Theorem orel2

Step	Hyp	Ref	Expression
1		idd 21	. 2 ⊢ (¬ 𝜑 → (𝜓 → 𝜓))
2		pm2.21 618	. 2 ⊢ (¬ 𝜑 → (𝜑 → 𝜓))
3	1, 2	jaod 719	1 ⊢ (¬ 𝜑 → ((𝜓 ∨ 𝜑) → 𝜓))

Syntax hints:  ¬ wn 3   → wi 4   ∨ wo 710

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in2 616  ax-io 711

This theorem depends on definitions:  df-bi 117

This theorem is referenced by:  biorfi  748  pm2.64  803  stdcn  849  pm5.71dc  964  ecased  1362  19.30dc  1651  dveeq2  1839  prel12  3814  funun  5320  fnpr2ob  13216