Theorem or4 675

Description: Rearrangement of 4 disjuncts. (Contributed by NM, 12-Aug-1994.)

Assertion

Ref	Expression
or4	⊢ (((φ ∨ ψ) ∨ (χ ∨ θ)) ↔ ((φ ∨ χ) ∨ (ψ ∨ θ)))

Proof of Theorem or4

Step	Hyp	Ref	Expression
1		or12 670	. . 3 ⊢ ((ψ ∨ (χ ∨ θ)) ↔ (χ ∨ (ψ ∨ θ)))
2	1	orbi2i 666	. 2 ⊢ ((φ ∨ (ψ ∨ (χ ∨ θ))) ↔ (φ ∨ (χ ∨ (ψ ∨ θ))))
3		orass 671	. 2 ⊢ (((φ ∨ ψ) ∨ (χ ∨ θ)) ↔ (φ ∨ (ψ ∨ (χ ∨ θ))))
4		orass 671	. 2 ⊢ (((φ ∨ χ) ∨ (ψ ∨ θ)) ↔ (φ ∨ (χ ∨ (ψ ∨ θ))))
5	2, 3, 4	3bitr4i 201	1 ⊢ (((φ ∨ ψ) ∨ (χ ∨ θ)) ↔ ((φ ∨ χ) ∨ (ψ ∨ θ)))

Syntax hints:   ↔ wb 98   ∨ wo 616

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 617

This theorem depends on definitions:  df-bi 110

This theorem is referenced by:  or42  676  orordi  677  orordir  678  3or6  1201  swoer  6041  apcotr  7198