Theorem imandc 820

Description: Express implication in terms of conjunction. Theorem 3.4(27) of [Stoll] p. 176, with an added decidability condition. The forward direction, imanim 819, holds for all propositions, not just decidable ones. (Contributed by Jim Kingdon, 25-Apr-2018.)

Assertion

Ref	Expression
imandc	|- (DECID ps -> ( ( ph -> ps ) <-> -. ( ph /\ -. ps ) ) )

Proof of Theorem imandc

Step	Hyp	Ref	Expression
1		notnotbdc 800	. . 3 |- (DECID ps -> ( ps <-> -. -. ps ) )
2	1	imbi2d 228	. 2 |- (DECID ps -> ( ( ph -> ps ) <-> ( ph -> -. -. ps ) ) )
3		imnan 657	. 2 |- ( ( ph -> -. -. ps ) <-> -. ( ph /\ -. ps ) )
4	2, 3	syl6bb 194	1 |- (DECID ps -> ( ( ph -> ps ) <-> -. ( ph /\ -. ps ) ) )

Syntax hints:   -. wn 3   -> wi 4   /\ wa 102   <-> wb 103  DECID wdc 776

This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-in1 577  ax-in2 578  ax-io 663

This theorem depends on definitions:  df-bi 115  df-dc 777

This theorem is referenced by:  annimdc  879  isprm3  10644