Theorem bitr3i

Description: An inference from transitive law for logical equivalence. (Contributed by NM, 2-Jun-1993)

	Ref	Expression
Hypotheses	bitr3i.1	$$⊢\psi \leftrightarrow \phi$$
	bitr3i.2	$$⊢\psi \leftrightarrow \chi$$
Assertion	bitr3i	$$⊢\phi \leftrightarrow \chi$$

Proof

Step	Hyp	Ref	Expression
1		bitr3i.1	$$⊢\psi \leftrightarrow \phi$$
2		bitr3i.2	$$⊢\psi \leftrightarrow \chi$$
3	1	bicomi	$$⊢\phi \leftrightarrow \psi$$
4	3 2	bitri	$$⊢\phi \leftrightarrow \chi$$