Theorem syl5bi

Description: A mixed syllogism inference from a nested implication and a biconditional. Useful for substituting an embedded antecedent with a definition. (Contributed by NM, 12-Jan-1993)

	Ref	Expression
Hypotheses	syl5bi.1	⊢ ( 𝜑 ↔ 𝜓 )
	syl5bi.2	⊢ ( 𝜒 → ( 𝜓 → 𝜃 ) )
Assertion	syl5bi	⊢ ( 𝜒 → ( 𝜑 → 𝜃 ) )

Proof

Step	Hyp	Ref	Expression
1		syl5bi.1	⊢ ( 𝜑 ↔ 𝜓 )
2		syl5bi.2	⊢ ( 𝜒 → ( 𝜓 → 𝜃 ) )
3	1	biimpi	⊢ ( 𝜑 → 𝜓 )
4	3 2	syl5	⊢ ( 𝜒 → ( 𝜑 → 𝜃 ) )