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Theorem preqsnd 4781
 Description: Equivalence for a pair equal to a singleton, deduction form. (Contributed by Thierry Arnoux, 27-Dec-2016.) (Revised by AV, 13-Jun-2022.)
Hypotheses
Ref Expression
preqsnd.1 (𝜑𝐴 ∈ V)
preqsnd.2 (𝜑𝐵 ∈ V)
Assertion
Ref Expression
preqsnd (𝜑 → ({𝐴, 𝐵} = {𝐶} ↔ (𝐴 = 𝐶𝐵 = 𝐶)))

Proof of Theorem preqsnd
StepHypRef Expression
1 preqsnd.1 . . . 4 (𝜑𝐴 ∈ V)
21adantl 484 . . 3 ((𝐶 ∈ V ∧ 𝜑) → 𝐴 ∈ V)
3 preqsnd.2 . . . 4 (𝜑𝐵 ∈ V)
43adantl 484 . . 3 ((𝐶 ∈ V ∧ 𝜑) → 𝐵 ∈ V)
5 simpl 485 . . 3 ((𝐶 ∈ V ∧ 𝜑) → 𝐶 ∈ V)
6 dfsn2 4572 . . . . 5 {𝐶} = {𝐶, 𝐶}
76eqeq2i 2832 . . . 4 ({𝐴, 𝐵} = {𝐶} ↔ {𝐴, 𝐵} = {𝐶, 𝐶})
8 preq12bg 4776 . . . . 5 (((𝐴 ∈ V ∧ 𝐵 ∈ V) ∧ (𝐶 ∈ V ∧ 𝐶 ∈ V)) → ({𝐴, 𝐵} = {𝐶, 𝐶} ↔ ((𝐴 = 𝐶𝐵 = 𝐶) ∨ (𝐴 = 𝐶𝐵 = 𝐶))))
9 oridm 900 . . . . 5 (((𝐴 = 𝐶𝐵 = 𝐶) ∨ (𝐴 = 𝐶𝐵 = 𝐶)) ↔ (𝐴 = 𝐶𝐵 = 𝐶))
108, 9syl6bb 289 . . . 4 (((𝐴 ∈ V ∧ 𝐵 ∈ V) ∧ (𝐶 ∈ V ∧ 𝐶 ∈ V)) → ({𝐴, 𝐵} = {𝐶, 𝐶} ↔ (𝐴 = 𝐶𝐵 = 𝐶)))
117, 10syl5bb 285 . . 3 (((𝐴 ∈ V ∧ 𝐵 ∈ V) ∧ (𝐶 ∈ V ∧ 𝐶 ∈ V)) → ({𝐴, 𝐵} = {𝐶} ↔ (𝐴 = 𝐶𝐵 = 𝐶)))
122, 4, 5, 5, 11syl22anc 836 . 2 ((𝐶 ∈ V ∧ 𝜑) → ({𝐴, 𝐵} = {𝐶} ↔ (𝐴 = 𝐶𝐵 = 𝐶)))
13 snprc 4645 . . . . . . 7 𝐶 ∈ V ↔ {𝐶} = ∅)
1413biimpi 218 . . . . . 6 𝐶 ∈ V → {𝐶} = ∅)
1514adantr 483 . . . . 5 ((¬ 𝐶 ∈ V ∧ 𝜑) → {𝐶} = ∅)
1615eqeq2d 2830 . . . 4 ((¬ 𝐶 ∈ V ∧ 𝜑) → ({𝐴, 𝐵} = {𝐶} ↔ {𝐴, 𝐵} = ∅))
17 prnzg 4705 . . . . . . 7 (𝐴 ∈ V → {𝐴, 𝐵} ≠ ∅)
18 eqneqall 3025 . . . . . . 7 ({𝐴, 𝐵} = ∅ → ({𝐴, 𝐵} ≠ ∅ → (𝐴 = 𝐶𝐵 = 𝐶)))
1917, 18syl5com 31 . . . . . 6 (𝐴 ∈ V → ({𝐴, 𝐵} = ∅ → (𝐴 = 𝐶𝐵 = 𝐶)))
201, 19syl 17 . . . . 5 (𝜑 → ({𝐴, 𝐵} = ∅ → (𝐴 = 𝐶𝐵 = 𝐶)))
2120adantl 484 . . . 4 ((¬ 𝐶 ∈ V ∧ 𝜑) → ({𝐴, 𝐵} = ∅ → (𝐴 = 𝐶𝐵 = 𝐶)))
2216, 21sylbid 242 . . 3 ((¬ 𝐶 ∈ V ∧ 𝜑) → ({𝐴, 𝐵} = {𝐶} → (𝐴 = 𝐶𝐵 = 𝐶)))
23 eleq1 2898 . . . . . . . . . 10 (𝐶 = 𝐴 → (𝐶 ∈ V ↔ 𝐴 ∈ V))
2423eqcoms 2827 . . . . . . . . 9 (𝐴 = 𝐶 → (𝐶 ∈ V ↔ 𝐴 ∈ V))
2524notbid 320 . . . . . . . 8 (𝐴 = 𝐶 → (¬ 𝐶 ∈ V ↔ ¬ 𝐴 ∈ V))
26 pm2.21 123 . . . . . . . 8 𝐴 ∈ V → (𝐴 ∈ V → (𝐵 = 𝐶 → {𝐴, 𝐵} = {𝐶})))
2725, 26syl6bi 255 . . . . . . 7 (𝐴 = 𝐶 → (¬ 𝐶 ∈ V → (𝐴 ∈ V → (𝐵 = 𝐶 → {𝐴, 𝐵} = {𝐶}))))
2827com13 88 . . . . . 6 (𝐴 ∈ V → (¬ 𝐶 ∈ V → (𝐴 = 𝐶 → (𝐵 = 𝐶 → {𝐴, 𝐵} = {𝐶}))))
291, 28syl 17 . . . . 5 (𝜑 → (¬ 𝐶 ∈ V → (𝐴 = 𝐶 → (𝐵 = 𝐶 → {𝐴, 𝐵} = {𝐶}))))
3029impcom 410 . . . 4 ((¬ 𝐶 ∈ V ∧ 𝜑) → (𝐴 = 𝐶 → (𝐵 = 𝐶 → {𝐴, 𝐵} = {𝐶})))
3130impd 413 . . 3 ((¬ 𝐶 ∈ V ∧ 𝜑) → ((𝐴 = 𝐶𝐵 = 𝐶) → {𝐴, 𝐵} = {𝐶}))
3222, 31impbid 214 . 2 ((¬ 𝐶 ∈ V ∧ 𝜑) → ({𝐴, 𝐵} = {𝐶} ↔ (𝐴 = 𝐶𝐵 = 𝐶)))
3312, 32pm2.61ian 810 1 (𝜑 → ({𝐴, 𝐵} = {𝐶} ↔ (𝐴 = 𝐶𝐵 = 𝐶)))
 Colors of variables: wff setvar class Syntax hints:  ¬ wn 3   → wi 4   ↔ wb 208   ∧ wa 398   ∨ wo 843   = wceq 1530   ∈ wcel 2107   ≠ wne 3014  Vcvv 3493  ∅c0 4289  {csn 4559  {cpr 4561 This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1789  ax-4 1803  ax-5 1904  ax-6 1963  ax-7 2008  ax-8 2109  ax-9 2117  ax-10 2138  ax-11 2153  ax-12 2169  ax-ext 2791 This theorem depends on definitions:  df-bi 209  df-an 399  df-or 844  df-3an 1083  df-tru 1533  df-ex 1774  df-nf 1778  df-sb 2063  df-clab 2798  df-cleq 2812  df-clel 2891  df-nfc 2961  df-ne 3015  df-v 3495  df-dif 3937  df-un 3939  df-nul 4290  df-sn 4560  df-pr 4562 This theorem is referenced by:  prnesn  4782  preqsn  4784  opeqsng  5384  1loopgrnb0  27276  disjdifprg  30317
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