Theorem pm2.73 719

Description: Theorem *2.73 of [WhiteheadRussell] p. 108. (Contributed by NM, 3-Jan-2005.)

Assertion

Ref	Expression
pm2.73	⊢ ((𝜑 → 𝜓) → (((𝜑 ∨ 𝜓) ∨ 𝜒) → (𝜓 ∨ 𝜒)))

Proof of Theorem pm2.73

Step	Hyp	Ref	Expression
1		pm2.621 666	. 2 ⊢ ((𝜑 → 𝜓) → ((𝜑 ∨ 𝜓) → 𝜓))
2	1	orim1d 701	1 ⊢ ((𝜑 → 𝜓) → (((𝜑 ∨ 𝜓) ∨ 𝜒) → (𝜓 ∨ 𝜒)))

Syntax hints:   → wi 4   ∨ wo 629

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-io 630

This theorem depends on definitions:  df-bi 110

This theorem is referenced by: (None)