Theorem pm2.36

Description: Theorem *2.36 of WhiteheadRussell p. 105. (Contributed by NM, 6-Mar-2008)

	Ref	Expression
Assertion	pm2.36	⊢ ( ( 𝜓 → 𝜒 ) → ( ( 𝜑 ∨ 𝜓 ) → ( 𝜒 ∨ 𝜑 ) ) )

Proof

Step	Hyp	Ref	Expression
1		pm1.4	⊢ ( ( 𝜑 ∨ 𝜓 ) → ( 𝜓 ∨ 𝜑 ) )
2		pm2.38	⊢ ( ( 𝜓 → 𝜒 ) → ( ( 𝜓 ∨ 𝜑 ) → ( 𝜒 ∨ 𝜑 ) ) )
3	1 2	syl5	⊢ ( ( 𝜓 → 𝜒 ) → ( ( 𝜑 ∨ 𝜓 ) → ( 𝜒 ∨ 𝜑 ) ) )