Theorem orordir 786

Description: Distribution of disjunction over disjunction. (Contributed by NM, 25-Feb-1995.)

Assertion

Ref	Expression
orordir	⊢ (((𝜑 ∨ 𝜓) ∨ 𝜒) ↔ ((𝜑 ∨ 𝜒) ∨ (𝜓 ∨ 𝜒)))

Proof of Theorem orordir

Step	Hyp	Ref	Expression
1		oridm 769	. . 3 ⊢ ((𝜒 ∨ 𝜒) ↔ 𝜒)
2	1	orbi2i 774	. 2 ⊢ (((𝜑 ∨ 𝜓) ∨ (𝜒 ∨ 𝜒)) ↔ ((𝜑 ∨ 𝜓) ∨ 𝜒))
3		or4 783	. 2 ⊢ (((𝜑 ∨ 𝜓) ∨ (𝜒 ∨ 𝜒)) ↔ ((𝜑 ∨ 𝜒) ∨ (𝜓 ∨ 𝜒)))
4	2, 3	bitr3i 186	1 ⊢ (((𝜑 ∨ 𝜓) ∨ 𝜒) ↔ ((𝜑 ∨ 𝜒) ∨ (𝜓 ∨ 𝜒)))

This proof depends on syntax axioms:   ↔ wb 105   ∨ wo 720

This proof depends on axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-io 721

This proof depends on definitions:  df-bi 117

This theorem is used by:  elznn0  9659