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Theorem eqssi 2961
 Description: Infer equality from two subclass relationships. Compare Theorem 4 of [Suppes] p. 22. (Contributed by NM, 9-Sep-1993.)
Hypotheses
Ref Expression
eqssi.1 𝐴𝐵
eqssi.2 𝐵𝐴
Assertion
Ref Expression
eqssi 𝐴 = 𝐵

Proof of Theorem eqssi
StepHypRef Expression
1 eqssi.1 . 2 𝐴𝐵
2 eqssi.2 . 2 𝐵𝐴
3 eqss 2960 . 2 (𝐴 = 𝐵 ↔ (𝐴𝐵𝐵𝐴))
41, 2, 3mpbir2an 849 1 𝐴 = 𝐵
 Colors of variables: wff set class Syntax hints:   = wceq 1243   ⊆ wss 2917 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 99  ax-ia2 100  ax-ia3 101  ax-5 1336  ax-7 1337  ax-gen 1338  ax-ie1 1382  ax-ie2 1383  ax-8 1395  ax-11 1397  ax-4 1400  ax-17 1419  ax-i9 1423  ax-ial 1427  ax-i5r 1428  ax-ext 2022 This theorem depends on definitions:  df-bi 110  df-nf 1350  df-sb 1646  df-clab 2027  df-cleq 2033  df-clel 2036  df-in 2924  df-ss 2931 This theorem is referenced by:  inv1  3253  unv  3254  undifabs  3300  intab  3644  intid  3960  find  4322  limom  4336  dmv  4551  0ima  4685  rnxpid  4755  dftpos4  5878  dfuzi  8348  unirnioo  8842
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