Theorem if0ab 16127

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 3657, |- ( A e. V -> if ( ph , A , (/) ) e. ~P A ), from which fmelpw1o 7428 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 3495	. . . . . 6 |- -. x e. (/)
2	1	intnanr 935	. . . . 5 |- -. ( x e. (/) /\ -. ph )
3	2	biorfi 751	. . . 4 |- ( ( x e. A /\ ph ) <-> ( ( x e. A /\ ph ) \/ ( x e. (/) /\ -. ph ) ) )
4	3	bicomi 132	. . 3 |- ( ( ( x e. A /\ ph ) \/ ( x e. (/) /\ -. ph ) ) <-> ( x e. A /\ ph ) )
5	4	abbii 2345	. 2 |- { x | ( ( x e. A /\ ph ) \/ ( x e. (/) /\ -. ph ) ) } = { x | ( x e. A /\ ph ) }
6		df-if 3603	. 2 |- if ( ph , A , (/) ) = { x | ( ( x e. A /\ ph ) \/ ( x e. (/) /\ -. ph ) ) }
7		df-rab 2517	. 2 |- { x e. A | ph } = { x | ( x e. A /\ ph ) }
8	5, 6, 7	3eqtr4i 2260	1 |- if ( ph , A , (/) ) = { x e. A | ph }

Syntax hints:   -. wn 3   /\ wa 104   \/ wo 713   = wceq 1395   e. wcel 2200   {cab 2215   {crab 2512   (/)c0 3491   ifcif 3602

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 714  ax-5 1493  ax-7 1494  ax-gen 1495  ax-ie1 1539  ax-ie2 1540  ax-8 1550  ax-10 1551  ax-11 1552  ax-i12 1553  ax-bndl 1555  ax-4 1556  ax-17 1572  ax-i9 1576  ax-ial 1580  ax-i5r 1581  ax-ext 2211

This theorem depends on definitions:  df-bi 117  df-tru 1398  df-nf 1507  df-sb 1809  df-clab 2216  df-cleq 2222  df-clel 2225  df-nfc 2361  df-rab 2517  df-v 2801  df-dif 3199  df-nul 3492  df-if 3603

This theorem is referenced by: (None)