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Theorem dmun 5253
 Description: The domain of a union is the union of domains. Exercise 56(a) of [Enderton] p. 65. (Contributed by NM, 12-Aug-1994.) (Proof shortened by Andrew Salmon, 27-Aug-2011.)
Assertion
Ref Expression
dmun dom (𝐴𝐵) = (dom 𝐴 ∪ dom 𝐵)

Proof of Theorem dmun
Dummy variables 𝑥 𝑦 are mutually distinct and distinct from all other variables.
StepHypRef Expression
1 unab 3853 . . 3 ({𝑦 ∣ ∃𝑥 𝑦𝐴𝑥} ∪ {𝑦 ∣ ∃𝑥 𝑦𝐵𝑥}) = {𝑦 ∣ (∃𝑥 𝑦𝐴𝑥 ∨ ∃𝑥 𝑦𝐵𝑥)}
2 brun 4633 . . . . . 6 (𝑦(𝐴𝐵)𝑥 ↔ (𝑦𝐴𝑥𝑦𝐵𝑥))
32exbii 1764 . . . . 5 (∃𝑥 𝑦(𝐴𝐵)𝑥 ↔ ∃𝑥(𝑦𝐴𝑥𝑦𝐵𝑥))
4 19.43 1799 . . . . 5 (∃𝑥(𝑦𝐴𝑥𝑦𝐵𝑥) ↔ (∃𝑥 𝑦𝐴𝑥 ∨ ∃𝑥 𝑦𝐵𝑥))
53, 4bitr2i 264 . . . 4 ((∃𝑥 𝑦𝐴𝑥 ∨ ∃𝑥 𝑦𝐵𝑥) ↔ ∃𝑥 𝑦(𝐴𝐵)𝑥)
65abbii 2726 . . 3 {𝑦 ∣ (∃𝑥 𝑦𝐴𝑥 ∨ ∃𝑥 𝑦𝐵𝑥)} = {𝑦 ∣ ∃𝑥 𝑦(𝐴𝐵)𝑥}
71, 6eqtri 2632 . 2 ({𝑦 ∣ ∃𝑥 𝑦𝐴𝑥} ∪ {𝑦 ∣ ∃𝑥 𝑦𝐵𝑥}) = {𝑦 ∣ ∃𝑥 𝑦(𝐴𝐵)𝑥}
8 df-dm 5048 . . 3 dom 𝐴 = {𝑦 ∣ ∃𝑥 𝑦𝐴𝑥}
9 df-dm 5048 . . 3 dom 𝐵 = {𝑦 ∣ ∃𝑥 𝑦𝐵𝑥}
108, 9uneq12i 3727 . 2 (dom 𝐴 ∪ dom 𝐵) = ({𝑦 ∣ ∃𝑥 𝑦𝐴𝑥} ∪ {𝑦 ∣ ∃𝑥 𝑦𝐵𝑥})
11 df-dm 5048 . 2 dom (𝐴𝐵) = {𝑦 ∣ ∃𝑥 𝑦(𝐴𝐵)𝑥}
127, 10, 113eqtr4ri 2643 1 dom (𝐴𝐵) = (dom 𝐴 ∪ dom 𝐵)
 Colors of variables: wff setvar class Syntax hints:   ∨ wo 382   = wceq 1475  ∃wex 1695  {cab 2596   ∪ cun 3538   class class class wbr 4583  dom cdm 5038 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1713  ax-4 1728  ax-5 1827  ax-6 1875  ax-7 1922  ax-10 2006  ax-11 2021  ax-12 2034  ax-13 2234  ax-ext 2590 This theorem depends on definitions:  df-bi 196  df-or 384  df-an 385  df-tru 1478  df-ex 1696  df-nf 1701  df-sb 1868  df-clab 2597  df-cleq 2603  df-clel 2606  df-nfc 2740  df-v 3175  df-un 3545  df-br 4584  df-dm 5048 This theorem is referenced by:  rnun  5460  dmpropg  5526  dmtpop  5529  fntpg  5862  fnun  5911  wfrlem13  7314  wfrlem16  7317  tfrlem10  7370  sbthlem5  7959  fodomr  7996  axdc3lem4  9158  hashfun  13084  s4dom  13514  dmtrclfv  13607  setsdm  15724  strlemor1  15796  strleun  15799  xpsfrnel2  16048  estrreslem2  16601  mvdco  17688  gsumzaddlem  18144  uhgrun  25740  upgrun  25784  umgrun  25786  bnj1416  30361  fixun  31186  rclexi  36941  rtrclex  36943  rtrclexi  36947  cnvrcl0  36951  dmtrcl  36953  dfrtrcl5  36955  dfrcl2  36985  dmtrclfvRP  37041  vtxdun  40696  1wlkp1  40890  eupthp1  41384
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