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Theorem sniota 6325
 Description: A class abstraction with a unique member can be expressed as a singleton. (Contributed by Mario Carneiro, 23-Dec-2016.)
Assertion
Ref Expression
sniota (∃!𝑥𝜑 → {𝑥𝜑} = {(℩𝑥𝜑)})

Proof of Theorem sniota
StepHypRef Expression
1 nfeu1 2673 . 2 𝑥∃!𝑥𝜑
2 nfab1 2981 . 2 𝑥{𝑥𝜑}
3 nfiota1 6295 . . 3 𝑥(℩𝑥𝜑)
43nfsn 4617 . 2 𝑥{(℩𝑥𝜑)}
5 iota1 6311 . . . 4 (∃!𝑥𝜑 → (𝜑 ↔ (℩𝑥𝜑) = 𝑥))
6 eqcom 2829 . . . 4 ((℩𝑥𝜑) = 𝑥𝑥 = (℩𝑥𝜑))
75, 6syl6bb 290 . . 3 (∃!𝑥𝜑 → (𝜑𝑥 = (℩𝑥𝜑)))
8 abid 2804 . . 3 (𝑥 ∈ {𝑥𝜑} ↔ 𝜑)
9 velsn 4555 . . 3 (𝑥 ∈ {(℩𝑥𝜑)} ↔ 𝑥 = (℩𝑥𝜑))
107, 8, 93bitr4g 317 . 2 (∃!𝑥𝜑 → (𝑥 ∈ {𝑥𝜑} ↔ 𝑥 ∈ {(℩𝑥𝜑)}))
111, 2, 4, 10eqrd 3961 1 (∃!𝑥𝜑 → {𝑥𝜑} = {(℩𝑥𝜑)})
 Colors of variables: wff setvar class Syntax hints:   → wi 4   = wceq 1538   ∈ wcel 2114  ∃!weu 2652  {cab 2800  {csn 4539  ℩cio 6291 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 1911  ax-6 1970  ax-7 2015  ax-8 2116  ax-9 2124  ax-10 2145  ax-11 2161  ax-12 2178  ax-ext 2794 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 2070  df-mo 2622  df-eu 2653  df-clab 2801  df-cleq 2815  df-clel 2894  df-nfc 2962  df-ral 3135  df-rex 3136  df-v 3471  df-sbc 3748  df-un 3913  df-in 3915  df-ss 3925  df-sn 4540  df-pr 4542  df-uni 4814  df-iota 6293 This theorem is referenced by:  snriota  7131  fnimasnd  39363
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