Theorem pm4.39

Description: Theorem *4.39 of WhiteheadRussell p. 118. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm4.39	⊢ ( ( ( 𝜑 ↔ 𝜒 ) ∧ ( 𝜓 ↔ 𝜃 ) ) → ( ( 𝜑 ∨ 𝜓 ) ↔ ( 𝜒 ∨ 𝜃 ) ) )

Proof

Step	Hyp	Ref	Expression
1		simpl	⊢ ( ( ( 𝜑 ↔ 𝜒 ) ∧ ( 𝜓 ↔ 𝜃 ) ) → ( 𝜑 ↔ 𝜒 ) )
2		simpr	⊢ ( ( ( 𝜑 ↔ 𝜒 ) ∧ ( 𝜓 ↔ 𝜃 ) ) → ( 𝜓 ↔ 𝜃 ) )
3	1 2	orbi12d	⊢ ( ( ( 𝜑 ↔ 𝜒 ) ∧ ( 𝜓 ↔ 𝜃 ) ) → ( ( 𝜑 ∨ 𝜓 ) ↔ ( 𝜒 ∨ 𝜃 ) ) )