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Theorem abv 3485
Description: The class of sets verifying a property is the universal class if and only if that property is a tautology. The reverse implication (bj-abv 35781) requires fewer axioms. (Contributed by BJ, 19-Mar-2021.) Avoid df-clel 2810, ax-8 2108. (Revised by Gino Giotto, 30-Aug-2024.) (Proof shortened by BJ, 30-Aug-2024.)
Assertion
Ref Expression
abv ({𝑥𝜑} = V ↔ ∀𝑥𝜑)

Proof of Theorem abv
Dummy variable 𝑦 is distinct from all other variables.
StepHypRef Expression
1 dfcleq 2725 . . 3 ({𝑥𝜑} = {𝑥 ∣ ⊤} ↔ ∀𝑦(𝑦 ∈ {𝑥𝜑} ↔ 𝑦 ∈ {𝑥 ∣ ⊤}))
2 vextru 2716 . . . . . 6 𝑦 ∈ {𝑥 ∣ ⊤}
32tbt 369 . . . . 5 (𝑦 ∈ {𝑥𝜑} ↔ (𝑦 ∈ {𝑥𝜑} ↔ 𝑦 ∈ {𝑥 ∣ ⊤}))
4 df-clab 2710 . . . . 5 (𝑦 ∈ {𝑥𝜑} ↔ [𝑦 / 𝑥]𝜑)
53, 4bitr3i 276 . . . 4 ((𝑦 ∈ {𝑥𝜑} ↔ 𝑦 ∈ {𝑥 ∣ ⊤}) ↔ [𝑦 / 𝑥]𝜑)
65albii 1821 . . 3 (∀𝑦(𝑦 ∈ {𝑥𝜑} ↔ 𝑦 ∈ {𝑥 ∣ ⊤}) ↔ ∀𝑦[𝑦 / 𝑥]𝜑)
71, 6bitri 274 . 2 ({𝑥𝜑} = {𝑥 ∣ ⊤} ↔ ∀𝑦[𝑦 / 𝑥]𝜑)
8 dfv2 3477 . . 3 V = {𝑥 ∣ ⊤}
98eqeq2i 2745 . 2 ({𝑥𝜑} = V ↔ {𝑥𝜑} = {𝑥 ∣ ⊤})
10 sb8v 2348 . 2 (∀𝑥𝜑 ↔ ∀𝑦[𝑦 / 𝑥]𝜑)
117, 9, 103bitr4i 302 1 ({𝑥𝜑} = V ↔ ∀𝑥𝜑)
Colors of variables: wff setvar class
Syntax hints:  wb 205  wal 1539   = wceq 1541  wtru 1542  [wsb 2067  wcel 2106  {cab 2709  Vcvv 3474
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 1913  ax-6 1971  ax-7 2011  ax-9 2116  ax-11 2154  ax-ext 2703
This theorem depends on definitions:  df-bi 206  df-an 397  df-tru 1544  df-ex 1782  df-sb 2068  df-clab 2710  df-cleq 2724  df-v 3476
This theorem is referenced by:  dfnf5  4377
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