Theorem dcbi 921

Description: An equivalence of two decidable propositions is decidable. (Contributed by Jim Kingdon, 12-Apr-2018.)

Assertion

Ref	Expression
dcbi	|- (DECID ph -> (DECID ps -> DECID ( ph <-> ps ) ) )

Proof of Theorem dcbi

Step	Hyp	Ref	Expression
1		dcim 827	. . 3 |- (DECID ph -> (DECID ps -> DECID ( ph -> ps ) ) )
2		dcim 827	. . . 4 |- (DECID ps -> (DECID ph -> DECID ( ps -> ph ) ) )
3	2	com12 30	. . 3 |- (DECID ph -> (DECID ps -> DECID ( ps -> ph ) ) )
4		dcan 919	. . 3 |- (DECID ( ph -> ps ) -> (DECID ( ps -> ph ) -> DECID ( ( ph -> ps ) /\ ( ps -> ph ) ) ) )
5	1, 3, 4	syl6c 66	. 2 |- (DECID ph -> (DECID ps -> DECID ( ( ph -> ps ) /\ ( ps -> ph ) ) ) )
6		dfbi2 386	. . 3 |- ( ( ph <-> ps ) <-> ( ( ph -> ps ) /\ ( ps -> ph ) ) )
7	6	dcbii 826	. 2 |- (DECID ( ph <-> ps ) <-> DECID ( ( ph -> ps ) /\ ( ps -> ph ) ) )
8	5, 7	syl6ibr 161	1 |- (DECID ph -> (DECID ps -> DECID ( ph <-> ps ) ) )

Syntax hints:   -> wi 4   /\ wa 103   <-> wb 104  DECID wdc 820

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 604  ax-in2 605  ax-io 699

This theorem depends on definitions:  df-bi 116  df-dc 821

This theorem is referenced by:  xor3dc  1366  pm5.15dc  1368  bilukdc  1375  xordidc  1378