Theorem bitr4d

Description: Deduction form of bitr4i . (Contributed by NM, 30-Jun-1993)

	Ref	Expression
Hypotheses	bitr4d.1	$$⊢\phi \to \left(\psi \leftrightarrow \chi \right)$$
	bitr4d.2	$$⊢\phi \to \left(\theta \leftrightarrow \chi \right)$$
Assertion	bitr4d	$$⊢\phi \to \left(\psi \leftrightarrow \theta \right)$$

Proof

Step	Hyp	Ref	Expression
1		bitr4d.1	$$⊢\phi \to \left(\psi \leftrightarrow \chi \right)$$
2		bitr4d.2	$$⊢\phi \to \left(\theta \leftrightarrow \chi \right)$$
3	2	bicomd	$$⊢\phi \to \left(\chi \leftrightarrow \theta \right)$$
4	1 3	bitrd	$$⊢\phi \to \left(\psi \leftrightarrow \theta \right)$$