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Theorem elprg 4387
 Description: A member of an unordered pair of classes is one or the other of them. Exercise 1 of [TakeutiZaring] p. 15, generalized. (Contributed by NM, 13-Sep-1995.)
Assertion
Ref Expression
elprg (𝐴𝑉 → (𝐴 ∈ {𝐵, 𝐶} ↔ (𝐴 = 𝐵𝐴 = 𝐶)))

Proof of Theorem elprg
Dummy variable 𝑥 is distinct from all other variables.
StepHypRef Expression
1 eqeq1 2801 . . 3 (𝑥 = 𝐴 → (𝑥 = 𝐵𝐴 = 𝐵))
2 eqeq1 2801 . . 3 (𝑥 = 𝐴 → (𝑥 = 𝐶𝐴 = 𝐶))
31, 2orbi12d 943 . 2 (𝑥 = 𝐴 → ((𝑥 = 𝐵𝑥 = 𝐶) ↔ (𝐴 = 𝐵𝐴 = 𝐶)))
4 dfpr2 4385 . 2 {𝐵, 𝐶} = {𝑥 ∣ (𝑥 = 𝐵𝑥 = 𝐶)}
53, 4elab2g 3543 1 (𝐴𝑉 → (𝐴 ∈ {𝐵, 𝐶} ↔ (𝐴 = 𝐵𝐴 = 𝐶)))
 Colors of variables: wff setvar class Syntax hints:   → wi 4   ↔ wb 198   ∨ wo 874   = wceq 1653   ∈ wcel 2157  {cpr 4368 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1891  ax-4 1905  ax-5 2006  ax-6 2072  ax-7 2107  ax-9 2166  ax-10 2185  ax-11 2200  ax-12 2213  ax-ext 2775 This theorem depends on definitions:  df-bi 199  df-an 386  df-or 875  df-tru 1657  df-ex 1876  df-nf 1880  df-sb 2065  df-clab 2784  df-cleq 2790  df-clel 2793  df-nfc 2928  df-v 3385  df-un 3772  df-sn 4367  df-pr 4369 This theorem is referenced by:  elpri  4388  elpr  4389  elpr2  4390  eldifpr  4394  eltpg  4415  ifpr  4421  prid1g  4482  ssprss  4541  preq1b  4561  prel12g  4582  ordunpr  7258  hashtpg  13512  cnsubrg  20124  atandm  24951  1egrvtxdg0  26752  eupth2lem1  27554  eliccioo  30146  nelpr2  40007  nelpr1  40008  sfprmdvdsmersenne  42289
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