Theorem notnotdOLD 305

Description: Obsolete proof of notnotd 138 as of 27-Mar-2021. (Contributed by Jarvin Udandy, 2-Sep-2016.) (New usage is discouraged.) (Proof modification is discouraged.)

Hypothesis

Ref	Expression
notnotdOLD.1	|- ( ph -> ps )

Assertion

Ref	Expression
notnotdOLD	|- ( ph -> -. -. ps )

Proof of Theorem notnotdOLD

Step	Hyp	Ref	Expression
1		notnotdOLD.1	. 2 |- ( ph -> ps )
2		notnotb 304	. 2 |- ( ps <-> -. -. ps )
3	1, 2	sylib 208	1 |- ( ph -> -. -. ps )

Syntax hints:   -. wn 3   -> wi 4

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8

This theorem depends on definitions:  df-bi 197

This theorem is referenced by: (None)