Theorem pm4.61

Description: Theorem *4.61 of WhiteheadRussell p. 120. (Contributed by NM, 3-Jan-2005)

	Ref	Expression
Assertion	pm4.61	⊢ ( ¬ ( 𝜑 → 𝜓 ) ↔ ( 𝜑 ∧ ¬ 𝜓 ) )

Proof

Step	Hyp	Ref	Expression
1		annim	⊢ ( ( 𝜑 ∧ ¬ 𝜓 ) ↔ ¬ ( 𝜑 → 𝜓 ) )
2	1	bicomi	⊢ ( ¬ ( 𝜑 → 𝜓 ) ↔ ( 𝜑 ∧ ¬ 𝜓 ) )