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Theorem dfiun2g 4941
 Description: Alternate definition of indexed union when 𝐵 is a set. Definition 15(a) of [Suppes] p. 44. (Contributed by NM, 23-Mar-2006.) (Proof shortened by Andrew Salmon, 25-Jul-2011.) (Proof shortened by Rohan Ridenour, 11-Aug-2023.)
Assertion
Ref Expression
dfiun2g (∀𝑥𝐴 𝐵𝐶 𝑥𝐴 𝐵 = {𝑦 ∣ ∃𝑥𝐴 𝑦 = 𝐵})
Distinct variable groups:   𝑦,𝐴   𝑦,𝐵   𝑥,𝑦
Allowed substitution hints:   𝐴(𝑥)   𝐵(𝑥)   𝐶(𝑥,𝑦)

Proof of Theorem dfiun2g
Dummy variable 𝑧 is distinct from all other variables.
StepHypRef Expression
1 nfra1 3213 . . . . . 6 𝑥𝑥𝐴 𝐵𝐶
2 rspa 3201 . . . . . . 7 ((∀𝑥𝐴 𝐵𝐶𝑥𝐴) → 𝐵𝐶)
3 clel3g 3640 . . . . . . 7 (𝐵𝐶 → (𝑧𝐵 ↔ ∃𝑦(𝑦 = 𝐵𝑧𝑦)))
42, 3syl 17 . . . . . 6 ((∀𝑥𝐴 𝐵𝐶𝑥𝐴) → (𝑧𝐵 ↔ ∃𝑦(𝑦 = 𝐵𝑧𝑦)))
51, 4rexbida 3310 . . . . 5 (∀𝑥𝐴 𝐵𝐶 → (∃𝑥𝐴 𝑧𝐵 ↔ ∃𝑥𝐴𝑦(𝑦 = 𝐵𝑧𝑦)))
6 rexcom4 3243 . . . . 5 (∃𝑥𝐴𝑦(𝑦 = 𝐵𝑧𝑦) ↔ ∃𝑦𝑥𝐴 (𝑦 = 𝐵𝑧𝑦))
75, 6syl6bb 290 . . . 4 (∀𝑥𝐴 𝐵𝐶 → (∃𝑥𝐴 𝑧𝐵 ↔ ∃𝑦𝑥𝐴 (𝑦 = 𝐵𝑧𝑦)))
8 r19.41v 3338 . . . . . 6 (∃𝑥𝐴 (𝑦 = 𝐵𝑧𝑦) ↔ (∃𝑥𝐴 𝑦 = 𝐵𝑧𝑦))
98exbii 1849 . . . . 5 (∃𝑦𝑥𝐴 (𝑦 = 𝐵𝑧𝑦) ↔ ∃𝑦(∃𝑥𝐴 𝑦 = 𝐵𝑧𝑦))
10 exancom 1862 . . . . 5 (∃𝑦(∃𝑥𝐴 𝑦 = 𝐵𝑧𝑦) ↔ ∃𝑦(𝑧𝑦 ∧ ∃𝑥𝐴 𝑦 = 𝐵))
119, 10bitri 278 . . . 4 (∃𝑦𝑥𝐴 (𝑦 = 𝐵𝑧𝑦) ↔ ∃𝑦(𝑧𝑦 ∧ ∃𝑥𝐴 𝑦 = 𝐵))
127, 11syl6bb 290 . . 3 (∀𝑥𝐴 𝐵𝐶 → (∃𝑥𝐴 𝑧𝐵 ↔ ∃𝑦(𝑧𝑦 ∧ ∃𝑥𝐴 𝑦 = 𝐵)))
13 eliun 4909 . . 3 (𝑧 𝑥𝐴 𝐵 ↔ ∃𝑥𝐴 𝑧𝐵)
14 eluniab 4839 . . 3 (𝑧 {𝑦 ∣ ∃𝑥𝐴 𝑦 = 𝐵} ↔ ∃𝑦(𝑧𝑦 ∧ ∃𝑥𝐴 𝑦 = 𝐵))
1512, 13, 143bitr4g 317 . 2 (∀𝑥𝐴 𝐵𝐶 → (𝑧 𝑥𝐴 𝐵𝑧 {𝑦 ∣ ∃𝑥𝐴 𝑦 = 𝐵}))
1615eqrdv 2822 1 (∀𝑥𝐴 𝐵𝐶 𝑥𝐴 𝐵 = {𝑦 ∣ ∃𝑥𝐴 𝑦 = 𝐵})
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ↔ wb 209   ∧ wa 399   = wceq 1538  ∃wex 1781   ∈ wcel 2115  {cab 2802  ∀wral 3133  ∃wrex 3134  ∪ cuni 4824  ∪ ciun 4905 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1797  ax-4 1811  ax-5 1912  ax-6 1971  ax-7 2016  ax-8 2117  ax-9 2125  ax-10 2146  ax-11 2162  ax-12 2179  ax-ext 2796 This theorem depends on definitions:  df-bi 210  df-an 400  df-or 845  df-tru 1541  df-ex 1782  df-nf 1786  df-sb 2071  df-clab 2803  df-cleq 2817  df-clel 2896  df-nfc 2964  df-ral 3138  df-rex 3139  df-v 3482  df-uni 4825  df-iun 4907 This theorem is referenced by:  dfiun2  4944  dfiun3g  5822  abnexg  7472  iunexg  7659  uniqs  8353  ac6num  9899  iunopn  21509  pnrmopn  21954  cncmp  22003  ptcmplem3  22665  iunmbl  24163  voliun  24164  sigaclcuni  31437  sigaclcu2  31439  sigaclci  31451  measvunilem  31531  meascnbl  31538  carsgclctunlem3  31638  uniqsALTV  35694
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