Theorem jcndOLD

Description: Obsolete version of jcnd as of 10-Apr-2024. (Contributed by Glauco Siliprandi, 11-Dec-2019) (New usage is discouraged.) (Proof modification is discouraged.)

	Ref	Expression
Hypotheses	jcndOLD.1	|- ( ph -> ps )
	jcndOLD.2	|- ( ph -> -. ch )
Assertion	jcndOLD	|- ( ph -> -. ( ps -> ch ) )

Proof

Step	Hyp	Ref	Expression
1		jcndOLD.1	|- ( ph -> ps )
2		jcndOLD.2	|- ( ph -> -. ch )
3	1 2	jc	|- ( ph -> -. ( ps -> -. -. ch ) )
4		notnotb	|- ( ch <-> -. -. ch )
5	4	imbi2i	|- ( ( ps -> ch ) <-> ( ps -> -. -. ch ) )
6	3 5	sylnibr	|- ( ph -> -. ( ps -> ch ) )