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Theorem eusv2i 5008
 Description: Two ways to express single-valuedness of a class expression 𝐴(𝑥). (Contributed by NM, 14-Oct-2010.) (Revised by Mario Carneiro, 18-Nov-2016.)
Assertion
Ref Expression
eusv2i (∃!𝑦𝑥 𝑦 = 𝐴 → ∃!𝑦𝑥 𝑦 = 𝐴)
Distinct variable groups:   𝑥,𝑦   𝑦,𝐴
Allowed substitution hint:   𝐴(𝑥)

Proof of Theorem eusv2i
StepHypRef Expression
1 nfeu1 2613 . . 3 𝑦∃!𝑦𝑥 𝑦 = 𝐴
2 nfcvd 2899 . . . . . 6 (∃!𝑦𝑥 𝑦 = 𝐴𝑥𝑦)
3 eusvnf 5006 . . . . . 6 (∃!𝑦𝑥 𝑦 = 𝐴𝑥𝐴)
42, 3nfeqd 2906 . . . . 5 (∃!𝑦𝑥 𝑦 = 𝐴 → Ⅎ𝑥 𝑦 = 𝐴)
54nfrd 1862 . . . 4 (∃!𝑦𝑥 𝑦 = 𝐴 → (∃𝑥 𝑦 = 𝐴 → ∀𝑥 𝑦 = 𝐴))
6 19.2 2054 . . . 4 (∀𝑥 𝑦 = 𝐴 → ∃𝑥 𝑦 = 𝐴)
75, 6impbid1 215 . . 3 (∃!𝑦𝑥 𝑦 = 𝐴 → (∃𝑥 𝑦 = 𝐴 ↔ ∀𝑥 𝑦 = 𝐴))
81, 7eubid 2621 . 2 (∃!𝑦𝑥 𝑦 = 𝐴 → (∃!𝑦𝑥 𝑦 = 𝐴 ↔ ∃!𝑦𝑥 𝑦 = 𝐴))
98ibir 257 1 (∃!𝑦𝑥 𝑦 = 𝐴 → ∃!𝑦𝑥 𝑦 = 𝐴)
 Colors of variables: wff setvar class Syntax hints:   → wi 4  ∀wal 1626   = wceq 1628  ∃wex 1849  ∃!weu 2603 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1867  ax-4 1882  ax-5 1984  ax-6 2050  ax-7 2086  ax-9 2144  ax-10 2164  ax-11 2179  ax-12 2192  ax-13 2387  ax-ext 2736 This theorem depends on definitions:  df-bi 197  df-or 384  df-an 385  df-tru 1631  df-fal 1634  df-ex 1850  df-nf 1855  df-sb 2043  df-eu 2607  df-clab 2743  df-cleq 2749  df-clel 2752  df-nfc 2887  df-v 3338  df-sbc 3573  df-csb 3671  df-dif 3714  df-nul 4055 This theorem is referenced by:  eusv2nf  5009
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