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Theorem zfun 6848
Description: Axiom of Union expressed with the fewest number of different variables. (Contributed by NM, 14-Aug-2003.)
Assertion
Ref Expression
zfun 𝑥𝑦(∃𝑥(𝑦𝑥𝑥𝑧) → 𝑦𝑥)
Distinct variable group:   𝑥,𝑦,𝑧

Proof of Theorem zfun
Dummy variable 𝑤 is distinct from all other variables.
StepHypRef Expression
1 ax-un 6847 . 2 𝑥𝑦(∃𝑤(𝑦𝑤𝑤𝑧) → 𝑦𝑥)
2 elequ2 1991 . . . . . . 7 (𝑤 = 𝑥 → (𝑦𝑤𝑦𝑥))
3 elequ1 1984 . . . . . . 7 (𝑤 = 𝑥 → (𝑤𝑧𝑥𝑧))
42, 3anbi12d 743 . . . . . 6 (𝑤 = 𝑥 → ((𝑦𝑤𝑤𝑧) ↔ (𝑦𝑥𝑥𝑧)))
54cbvexv 2263 . . . . 5 (∃𝑤(𝑦𝑤𝑤𝑧) ↔ ∃𝑥(𝑦𝑥𝑥𝑧))
65imbi1i 338 . . . 4 ((∃𝑤(𝑦𝑤𝑤𝑧) → 𝑦𝑥) ↔ (∃𝑥(𝑦𝑥𝑥𝑧) → 𝑦𝑥))
76albii 1737 . . 3 (∀𝑦(∃𝑤(𝑦𝑤𝑤𝑧) → 𝑦𝑥) ↔ ∀𝑦(∃𝑥(𝑦𝑥𝑥𝑧) → 𝑦𝑥))
87exbii 1764 . 2 (∃𝑥𝑦(∃𝑤(𝑦𝑤𝑤𝑧) → 𝑦𝑥) ↔ ∃𝑥𝑦(∃𝑥(𝑦𝑥𝑥𝑧) → 𝑦𝑥))
91, 8mpbi 219 1 𝑥𝑦(∃𝑥(𝑦𝑥𝑥𝑧) → 𝑦𝑥)
Colors of variables: wff setvar class
Syntax hints:  wi 4  wa 383  wal 1473  wex 1695
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-8 1979  ax-9 1986  ax-10 2006  ax-11 2021  ax-12 2034  ax-13 2234  ax-un 6847
This theorem depends on definitions:  df-bi 196  df-an 385  df-ex 1696  df-nf 1701
This theorem is referenced by:  uniex2  6850  axunndlem1  9296
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