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Theorem 2rexsb 39819
 Description: An equivalent expression for double restricted existence, analogous to rexsb 39817. (Contributed by Alexander van der Vekens, 1-Jul-2017.)
Assertion
Ref Expression
2rexsb (∃𝑥𝐴𝑦𝐵 𝜑 ↔ ∃𝑧𝐴𝑤𝐵𝑥𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑))
Distinct variable groups:   𝑥,𝑤,𝑦,𝑧,𝐵   𝑤,𝐴,𝑥,𝑧   𝜑,𝑧,𝑤
Allowed substitution hints:   𝜑(𝑥,𝑦)   𝐴(𝑦)

Proof of Theorem 2rexsb
StepHypRef Expression
1 rexsb 39817 . . . 4 (∃𝑦𝐵 𝜑 ↔ ∃𝑤𝐵𝑦(𝑦 = 𝑤𝜑))
21rexbii 3023 . . 3 (∃𝑥𝐴𝑦𝐵 𝜑 ↔ ∃𝑥𝐴𝑤𝐵𝑦(𝑦 = 𝑤𝜑))
3 rexcom 3080 . . 3 (∃𝑥𝐴𝑤𝐵𝑦(𝑦 = 𝑤𝜑) ↔ ∃𝑤𝐵𝑥𝐴𝑦(𝑦 = 𝑤𝜑))
42, 3bitri 263 . 2 (∃𝑥𝐴𝑦𝐵 𝜑 ↔ ∃𝑤𝐵𝑥𝐴𝑦(𝑦 = 𝑤𝜑))
5 rexsb 39817 . . . . 5 (∃𝑥𝐴𝑦(𝑦 = 𝑤𝜑) ↔ ∃𝑧𝐴𝑥(𝑥 = 𝑧 → ∀𝑦(𝑦 = 𝑤𝜑)))
6 impexp 461 . . . . . . . . 9 (((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑) ↔ (𝑥 = 𝑧 → (𝑦 = 𝑤𝜑)))
76albii 1737 . . . . . . . 8 (∀𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑) ↔ ∀𝑦(𝑥 = 𝑧 → (𝑦 = 𝑤𝜑)))
8 19.21v 1855 . . . . . . . 8 (∀𝑦(𝑥 = 𝑧 → (𝑦 = 𝑤𝜑)) ↔ (𝑥 = 𝑧 → ∀𝑦(𝑦 = 𝑤𝜑)))
97, 8bitr2i 264 . . . . . . 7 ((𝑥 = 𝑧 → ∀𝑦(𝑦 = 𝑤𝜑)) ↔ ∀𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑))
109albii 1737 . . . . . 6 (∀𝑥(𝑥 = 𝑧 → ∀𝑦(𝑦 = 𝑤𝜑)) ↔ ∀𝑥𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑))
1110rexbii 3023 . . . . 5 (∃𝑧𝐴𝑥(𝑥 = 𝑧 → ∀𝑦(𝑦 = 𝑤𝜑)) ↔ ∃𝑧𝐴𝑥𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑))
125, 11bitri 263 . . . 4 (∃𝑥𝐴𝑦(𝑦 = 𝑤𝜑) ↔ ∃𝑧𝐴𝑥𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑))
1312rexbii 3023 . . 3 (∃𝑤𝐵𝑥𝐴𝑦(𝑦 = 𝑤𝜑) ↔ ∃𝑤𝐵𝑧𝐴𝑥𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑))
14 rexcom 3080 . . 3 (∃𝑤𝐵𝑧𝐴𝑥𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑) ↔ ∃𝑧𝐴𝑤𝐵𝑥𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑))
1513, 14bitri 263 . 2 (∃𝑤𝐵𝑥𝐴𝑦(𝑦 = 𝑤𝜑) ↔ ∃𝑧𝐴𝑤𝐵𝑥𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑))
164, 15bitri 263 1 (∃𝑥𝐴𝑦𝐵 𝜑 ↔ ∃𝑧𝐴𝑤𝐵𝑥𝑦((𝑥 = 𝑧𝑦 = 𝑤) → 𝜑))
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ↔ wb 195   ∧ wa 383  ∀wal 1473  ∃wrex 2897 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-cleq 2603  df-clel 2606  df-nfc 2740  df-ral 2901  df-rex 2902 This theorem is referenced by: (None)
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