Theorem orel2 738

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		pm2.21 626	. 2 ⊢ (¬ 𝜑 → (𝜑 → 𝜓))
3	1, 2	jaod 729	1 ⊢ (¬ 𝜑 → ((𝜓 ∨ 𝜑) → 𝜓))

Syntax hints:  ¬ wn 3   → wi 4   ∨ wo 720

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 624  ax-io 721

This theorem depends on definitions:  df-bi 117

This theorem is referenced by:  biorfi  758  pm2.64  813  stdcn  859  pm5.71dc  974  ecased  1390  19.30dc  1680  dveeq2  1868  prel12  3894  funun  5420  fnpr2ob  13644