Theorem pm5.13

Description: Theorem *5.13 of WhiteheadRussell p. 123. (Contributed by NM, 3-Jan-2005) (Proof shortened by Wolf Lammen, 14-Nov-2012)

	Ref	Expression
Assertion	pm5.13	⊢ ( ( 𝜑 → 𝜓 ) ∨ ( 𝜓 → 𝜑 ) )

Proof

Step	Hyp	Ref	Expression
1		pm5.14	⊢ ( ( 𝜑 → 𝜓 ) ∨ ( 𝜓 → 𝜑 ) )