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Theorem ersym 7907
Description: An equivalence relation is symmetric. (Contributed by NM, 4-Jun-1995.) (Revised by Mario Carneiro, 12-Aug-2015.)
Hypotheses
Ref Expression
ersym.1 (𝜑𝑅 Er 𝑋)
ersym.2 (𝜑𝐴𝑅𝐵)
Assertion
Ref Expression
ersym (𝜑𝐵𝑅𝐴)

Proof of Theorem ersym
StepHypRef Expression
1 ersym.2 . . 3 (𝜑𝐴𝑅𝐵)
2 ersym.1 . . . . . 6 (𝜑𝑅 Er 𝑋)
3 errel 7904 . . . . . 6 (𝑅 Er 𝑋 → Rel 𝑅)
42, 3syl 17 . . . . 5 (𝜑 → Rel 𝑅)
5 brrelex12 5295 . . . . 5 ((Rel 𝑅𝐴𝑅𝐵) → (𝐴 ∈ V ∧ 𝐵 ∈ V))
64, 1, 5syl2anc 565 . . . 4 (𝜑 → (𝐴 ∈ V ∧ 𝐵 ∈ V))
7 brcnvg 5441 . . . . 5 ((𝐵 ∈ V ∧ 𝐴 ∈ V) → (𝐵𝑅𝐴𝐴𝑅𝐵))
87ancoms 455 . . . 4 ((𝐴 ∈ V ∧ 𝐵 ∈ V) → (𝐵𝑅𝐴𝐴𝑅𝐵))
96, 8syl 17 . . 3 (𝜑 → (𝐵𝑅𝐴𝐴𝑅𝐵))
101, 9mpbird 247 . 2 (𝜑𝐵𝑅𝐴)
11 df-er 7895 . . . . . 6 (𝑅 Er 𝑋 ↔ (Rel 𝑅 ∧ dom 𝑅 = 𝑋 ∧ (𝑅 ∪ (𝑅𝑅)) ⊆ 𝑅))
1211simp3bi 1140 . . . . 5 (𝑅 Er 𝑋 → (𝑅 ∪ (𝑅𝑅)) ⊆ 𝑅)
132, 12syl 17 . . . 4 (𝜑 → (𝑅 ∪ (𝑅𝑅)) ⊆ 𝑅)
1413unssad 3939 . . 3 (𝜑𝑅𝑅)
1514ssbrd 4827 . 2 (𝜑 → (𝐵𝑅𝐴𝐵𝑅𝐴))
1610, 15mpd 15 1 (𝜑𝐵𝑅𝐴)
Colors of variables: wff setvar class
Syntax hints:  wi 4  wb 196  wa 382   = wceq 1630  wcel 2144  Vcvv 3349  cun 3719  wss 3721   class class class wbr 4784  ccnv 5248  dom cdm 5249  ccom 5253  Rel wrel 5254   Er wer 7892
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1869  ax-4 1884  ax-5 1990  ax-6 2056  ax-7 2092  ax-9 2153  ax-10 2173  ax-11 2189  ax-12 2202  ax-13 2407  ax-ext 2750  ax-sep 4912  ax-nul 4920  ax-pr 5034
This theorem depends on definitions:  df-bi 197  df-an 383  df-or 827  df-3an 1072  df-tru 1633  df-ex 1852  df-nf 1857  df-sb 2049  df-eu 2621  df-mo 2622  df-clab 2757  df-cleq 2763  df-clel 2766  df-nfc 2901  df-ral 3065  df-rex 3066  df-rab 3069  df-v 3351  df-dif 3724  df-un 3726  df-in 3728  df-ss 3735  df-nul 4062  df-if 4224  df-sn 4315  df-pr 4317  df-op 4321  df-br 4785  df-opab 4845  df-xp 5255  df-rel 5256  df-cnv 5257  df-er 7895
This theorem is referenced by:  ercl2  7908  ersymb  7909  ertr2d  7912  ertr3d  7913  ertr4d  7914  erth  7942  erinxp  7972  nqereu  9952  nqerf  9953  1nqenq  9985  qusgrp2  17740  efginvrel2  18346  efgcpbllemb  18374  2idlcpbl  19448  tgptsmscls  22172
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