Theorem ifnebibdc 3628

Description: The converse of ifbi 3603 holds if the two values are not equal. (Contributed by Thierry Arnoux, 20-Feb-2025.)

Assertion

Ref	Expression
ifnebibdc	|- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( if ( ph , A , B ) = if ( ps , A , B ) <-> ( ph <-> ps ) ) )

Proof of Theorem ifnebibdc

Step	Hyp	Ref	Expression
1		eqifdc 3619	. . . 4 |- (DECID ps -> ( if ( ph , A , B ) = if ( ps , A , B ) <-> ( ( ps /\ if ( ph , A , B ) = A ) \/ ( -. ps /\ if ( ph , A , B ) = B ) ) ) )
2	1	3ad2ant2 1024	. . 3 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( if ( ph , A , B ) = if ( ps , A , B ) <-> ( ( ps /\ if ( ph , A , B ) = A ) \/ ( -. ps /\ if ( ph , A , B ) = B ) ) ) )
3		ifnetruedc 3626	. . . . . . . . 9 |- ( (DECID ph /\ A =/= B /\ if ( ph , A , B ) = A ) -> ph )
4	3	3expia 1210	. . . . . . . 8 |- ( (DECID ph /\ A =/= B ) -> ( if ( ph , A , B ) = A -> ph ) )
5	4	3adant2 1021	. . . . . . 7 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( if ( ph , A , B ) = A -> ph ) )
6	5	adantld 278	. . . . . 6 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( ( ps /\ if ( ph , A , B ) = A ) -> ph ) )
7		simpl 109	. . . . . 6 |- ( ( ps /\ if ( ph , A , B ) = A ) -> ps )
8	6, 7	jca2 308	. . . . 5 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( ( ps /\ if ( ph , A , B ) = A ) -> ( ph /\ ps ) ) )
9		pm5.1 603	. . . . 5 |- ( ( ph /\ ps ) -> ( ph <-> ps ) )
10	8, 9	syl6 33	. . . 4 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( ( ps /\ if ( ph , A , B ) = A ) -> ( ph <-> ps ) ) )
11		ifnefals 3627	. . . . . . . . 9 |- ( ( A =/= B /\ if ( ph , A , B ) = B ) -> -. ph )
12	11	ex 115	. . . . . . . 8 |- ( A =/= B -> ( if ( ph , A , B ) = B -> -. ph ) )
13	12	3ad2ant3 1025	. . . . . . 7 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( if ( ph , A , B ) = B -> -. ph ) )
14	13	adantld 278	. . . . . 6 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( ( -. ps /\ if ( ph , A , B ) = B ) -> -. ph ) )
15		simpl 109	. . . . . 6 |- ( ( -. ps /\ if ( ph , A , B ) = B ) -> -. ps )
16	14, 15	jca2 308	. . . . 5 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( ( -. ps /\ if ( ph , A , B ) = B ) -> ( -. ph /\ -. ps ) ) )
17		pm5.21 699	. . . . 5 |- ( ( -. ph /\ -. ps ) -> ( ph <-> ps ) )
18	16, 17	syl6 33	. . . 4 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( ( -. ps /\ if ( ph , A , B ) = B ) -> ( ph <-> ps ) ) )
19	10, 18	jaod 721	. . 3 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( ( ( ps /\ if ( ph , A , B ) = A ) \/ ( -. ps /\ if ( ph , A , B ) = B ) ) -> ( ph <-> ps ) ) )
20	2, 19	sylbid 150	. 2 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( if ( ph , A , B ) = if ( ps , A , B ) -> ( ph <-> ps ) ) )
21		ifbi 3603	. 2 |- ( ( ph <-> ps ) -> if ( ph , A , B ) = if ( ps , A , B ) )
22	20, 21	impbid1 142	1 |- ( (DECID ph /\ DECID ps /\ A =/= B ) -> ( if ( ph , A , B ) = if ( ps , A , B ) <-> ( ph <-> ps ) ) )

Syntax hints:   -. wn 3   -> wi 4   /\ wa 104   <-> wb 105   \/ wo 712  DECID wdc 838   /\ w3a 983   = wceq 1375   =/= wne 2380   ifcif 3582

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 617  ax-in2 618  ax-io 713  ax-5 1473  ax-7 1474  ax-gen 1475  ax-ie1 1519  ax-ie2 1520  ax-8 1530  ax-11 1532  ax-4 1536  ax-17 1552  ax-i9 1556  ax-ial 1560  ax-i5r 1561  ax-ext 2191

This theorem depends on definitions:  df-bi 117  df-dc 839  df-3an 985  df-tru 1378  df-nf 1487  df-sb 1789  df-clab 2196  df-cleq 2202  df-clel 2205  df-ne 2381  df-if 3583

This theorem is referenced by:  nninfinf  10632