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Theorem nfiu1 3687
 Description: Bound-variable hypothesis builder for indexed union. (Contributed by NM, 12-Oct-2003.)
Assertion
Ref Expression
nfiu1 𝑥 𝑥𝐴 𝐵

Proof of Theorem nfiu1
Dummy variable 𝑦 is distinct from all other variables.
StepHypRef Expression
1 df-iun 3659 . 2 𝑥𝐴 𝐵 = {𝑦 ∣ ∃𝑥𝐴 𝑦𝐵}
2 nfre1 2365 . . 3 𝑥𝑥𝐴 𝑦𝐵
32nfab 2182 . 2 𝑥{𝑦 ∣ ∃𝑥𝐴 𝑦𝐵}
41, 3nfcxfr 2175 1 𝑥 𝑥𝐴 𝐵
 Colors of variables: wff set class Syntax hints:   ∈ wcel 1393  {cab 2026  Ⅎwnfc 2165  ∃wrex 2307  ∪ ciun 3657 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-io 630  ax-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-10 1396  ax-11 1397  ax-i12 1398  ax-bndl 1399  ax-4 1400  ax-17 1419  ax-i9 1423  ax-ial 1427  ax-i5r 1428  ax-ext 2022 This theorem depends on definitions:  df-bi 110  df-nf 1350  df-sb 1646  df-clab 2027  df-cleq 2033  df-clel 2036  df-nfc 2167  df-rex 2312  df-iun 3659 This theorem is referenced by:  ssiun2s  3701  triun  3867  eliunxp  4475  opeliunxp2  4476
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