Theorem con1bid

Description: A contraposition deduction. (Contributed by NM, 9-Oct-1999)

	Ref	Expression
Hypothesis	con1bid.1	|- ( ph -> ( -. ps <-> ch ) )
Assertion	con1bid	|- ( ph -> ( -. ch <-> ps ) )

Proof

Step	Hyp	Ref	Expression
1		con1bid.1	|- ( ph -> ( -. ps <-> ch ) )
2	1	bicomd	|- ( ph -> ( ch <-> -. ps ) )
3	2	con2bid	|- ( ph -> ( ps <-> -. ch ) )
4	3	bicomd	|- ( ph -> ( -. ch <-> ps ) )