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Theorem ceqsex 3239
 Description: Elimination of an existential quantifier, using implicit substitution. (Contributed by NM, 2-Mar-1995.) (Revised by Mario Carneiro, 10-Oct-2016.)
Hypotheses
Ref Expression
ceqsex.1 𝑥𝜓
ceqsex.2 𝐴 ∈ V
ceqsex.3 (𝑥 = 𝐴 → (𝜑𝜓))
Assertion
Ref Expression
ceqsex (∃𝑥(𝑥 = 𝐴𝜑) ↔ 𝜓)
Distinct variable group:   𝑥,𝐴
Allowed substitution hints:   𝜑(𝑥)   𝜓(𝑥)

Proof of Theorem ceqsex
StepHypRef Expression
1 ceqsex.1 . . 3 𝑥𝜓
2 ceqsex.3 . . . 4 (𝑥 = 𝐴 → (𝜑𝜓))
32biimpa 501 . . 3 ((𝑥 = 𝐴𝜑) → 𝜓)
41, 3exlimi 2085 . 2 (∃𝑥(𝑥 = 𝐴𝜑) → 𝜓)
52biimprcd 240 . . . 4 (𝜓 → (𝑥 = 𝐴𝜑))
61, 5alrimi 2081 . . 3 (𝜓 → ∀𝑥(𝑥 = 𝐴𝜑))
7 ceqsex.2 . . . 4 𝐴 ∈ V
87isseti 3207 . . 3 𝑥 𝑥 = 𝐴
9 exintr 1818 . . 3 (∀𝑥(𝑥 = 𝐴𝜑) → (∃𝑥 𝑥 = 𝐴 → ∃𝑥(𝑥 = 𝐴𝜑)))
106, 8, 9mpisyl 21 . 2 (𝜓 → ∃𝑥(𝑥 = 𝐴𝜑))
114, 10impbii 199 1 (∃𝑥(𝑥 = 𝐴𝜑) ↔ 𝜓)
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ↔ wb 196   ∧ wa 384  ∀wal 1480   = wceq 1482  ∃wex 1703  Ⅎwnf 1707   ∈ wcel 1989  Vcvv 3198 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1721  ax-4 1736  ax-5 1838  ax-6 1887  ax-7 1934  ax-9 1998  ax-12 2046  ax-ext 2601 This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-tru 1485  df-ex 1704  df-nf 1709  df-sb 1880  df-clab 2608  df-cleq 2614  df-clel 2617  df-v 3200 This theorem is referenced by:  ceqsexv  3240  ceqsex2  3242
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