Theorem eluni 4870

Description: Membership in class union. (Contributed by NM, 22-May-1994.)

Assertion

Ref	Expression
eluni	⊢ (𝐴 ∈ ∪ 𝐵 ↔ ∃𝑥(𝐴 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵))

Distinct variable groups:   𝑥,𝐴   𝑥,𝐵

Proof of Theorem eluni

Dummy variable 𝑦 is distinct from all other variables.

Step	Hyp	Ref	Expression
1		elex 3478	. 2 ⊢ (𝐴 ∈ ∪ 𝐵 → 𝐴 ∈ V)
2		elex 3478	. . . 4 ⊢ (𝐴 ∈ 𝑥 → 𝐴 ∈ V)
3	2	adantr 485	. . 3 ⊢ ((𝐴 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵) → 𝐴 ∈ V)
4	3	exlimiv 1953	. 2 ⊢ (∃𝑥(𝐴 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵) → 𝐴 ∈ V)
5		eleq1 2853	. . . . 5 ⊢ (𝑦 = 𝐴 → (𝑦 ∈ 𝑥 ↔ 𝐴 ∈ 𝑥))
6	5	anbi1d 642	. . . 4 ⊢ (𝑦 = 𝐴 → ((𝑦 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵) ↔ (𝐴 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵)))
7	6	exbidv 1944	. . 3 ⊢ (𝑦 = 𝐴 → (∃𝑥(𝑦 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵) ↔ ∃𝑥(𝐴 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵)))
8		df-uni 4868	. . 3 ⊢ ∪ 𝐵 = {𝑦 ∣ ∃𝑥(𝑦 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵)}
9	7, 8	elab2g 3642	. 2 ⊢ (𝐴 ∈ V → (𝐴 ∈ ∪ 𝐵 ↔ ∃𝑥(𝐴 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵)))
10	1, 4, 9	pm5.21nii 381	1 ⊢ (𝐴 ∈ ∪ 𝐵 ↔ ∃𝑥(𝐴 ∈ 𝑥 ∧ 𝑥 ∈ 𝐵))

Syntax hints:   ↔ wb 209   ∧ wa 400   = wceq 1563  ∃wex 1802   ∈ wcel 2145  Vcvv 3457  ∪ cuni 4867

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1818  ax-4 1832  ax-5 1933  ax-6 1990  ax-7 2031  ax-8 2147  ax-9 2155  ax-ext 2737

This theorem depends on definitions:  df-bi 210  df-an 401  df-tru 1566  df-ex 1803  df-sb 2094  df-clab 2744  df-cleq 2757  df-clel 2840  df-v 3459  df-uni 4868

This theorem is referenced by:  eluni2  4871  elunii  4872  uniss  4875  eluniab  4881  uniun  4890  uniinOLD  4892  uni0  4896  unissb  4901  dfiun2g  4989  dftr2  5213  unipw  5421  dmuni  5894  iotanul2  6498  fununi  6600  elunirn  7239  uniex2  7725  uniuni  7749  mpoxopxnop0  8199  fprresex  8295  tfrlem7  8358  tfrlem9a  8361  inf2  9580  inf3lem2  9586  rankwflemb  9753  cardprclem  9953  carduni  9955  iunfictbso  10086  kmlem3  10124  kmlem4  10125  cfub  10220  isf34lem4  10349  grothtsk  10808  suplem1pr  11025  lidlunin0  21327  toprntopon  23039  isbasis2g  23062  tgval2  23070  ntreq0  23191  cmpsublem  23513  cmpsub  23514  cmpcld  23516  is1stc2  23556  alexsubALTlem3  24163  alexsubALT  24165  elold  28006  fnessref  36725  mh-infprim1bi  36914  bj-restuni  37594  difunieq  37875  ismnushort  44870  truniALT  45109  truniALTVD  45445  unisnALT  45493  uniclaxun  45554  elunif  45595  ssfiunibd  45887  stoweidlem27  46600  stoweidlem48  46621  setrec1lem3  50319  setrec1  50321