Theorem bitr4d

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

	Ref	Expression
Hypotheses	bitr4d.1	|- ( ph -> ( ps <-> ch ) )
	bitr4d.2	|- ( ph -> ( th <-> ch ) )
Assertion	bitr4d	|- ( ph -> ( ps <-> th ) )

Proof

Step	Hyp	Ref	Expression
1		bitr4d.1	|- ( ph -> ( ps <-> ch ) )
2		bitr4d.2	|- ( ph -> ( th <-> ch ) )
3	2	bicomd	|- ( ph -> ( ch <-> th ) )
4	1 3	bitrd	|- ( ph -> ( ps <-> th ) )