Theorem if0ab 13422

Description: Expression of a conditional class as a class abstraction when the False alternative is the empty class: in that case, the conditional class is the extension, in the True alternative, of the condition.

Remark: a consequence which could be formalized is the inclusion |- if ( ph , A , (/) ) C_ A and therefore, using elpwg 3551, |- ( A e. V -> if ( ph , A , (/) ) e. ~P A ), from which fmelpw1o 13423 could be derived, yielding an alternative proof. (Contributed by BJ, 16-Aug-2024.)

Assertion

Ref	Expression
if0ab	|- if ( ph , A , (/) ) = { x e. A | ph }

Distinct variable groups:   x, A   ph, x

Proof of Theorem if0ab

Step	Hyp	Ref	Expression
1		noel 3398	. . . . . 6 |- -. x e. (/)
2	1	intnanr 916	. . . . 5 |- -. ( x e. (/) /\ -. ph )
3	2	biorfi 736	. . . 4 |- ( ( x e. A /\ ph ) <-> ( ( x e. A /\ ph ) \/ ( x e. (/) /\ -. ph ) ) )
4	3	bicomi 131	. . 3 |- ( ( ( x e. A /\ ph ) \/ ( x e. (/) /\ -. ph ) ) <-> ( x e. A /\ ph ) )
5	4	abbii 2273	. 2 |- { x | ( ( x e. A /\ ph ) \/ ( x e. (/) /\ -. ph ) ) } = { x | ( x e. A /\ ph ) }
6		df-if 3506	. 2 |- if ( ph , A , (/) ) = { x | ( ( x e. A /\ ph ) \/ ( x e. (/) /\ -. ph ) ) }
7		df-rab 2444	. 2 |- { x e. A | ph } = { x | ( x e. A /\ ph ) }
8	5, 6, 7	3eqtr4i 2188	1 |- if ( ph , A , (/) ) = { x e. A | ph }

Syntax hints:   -. wn 3   /\ wa 103   \/ wo 698   = wceq 1335   e. wcel 2128   {cab 2143   {crab 2439   (/)c0 3394   ifcif 3505

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  ax-5 1427  ax-7 1428  ax-gen 1429  ax-ie1 1473  ax-ie2 1474  ax-8 1484  ax-10 1485  ax-11 1486  ax-i12 1487  ax-bndl 1489  ax-4 1490  ax-17 1506  ax-i9 1510  ax-ial 1514  ax-i5r 1515  ax-ext 2139

This theorem depends on definitions:  df-bi 116  df-tru 1338  df-nf 1441  df-sb 1743  df-clab 2144  df-cleq 2150  df-clel 2153  df-nfc 2288  df-rab 2444  df-v 2714  df-dif 3104  df-nul 3395  df-if 3506

This theorem is referenced by: (None)