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Theorem 3sstr4d 3067
Description: Substitution of equality into both sides of a subclass relationship. (Contributed by NM, 30-Nov-1995.) (Proof shortened by Eric Schmidt, 26-Jan-2007.)
Hypotheses
Ref Expression
3sstr4d.1 (𝜑𝐴𝐵)
3sstr4d.2 (𝜑𝐶 = 𝐴)
3sstr4d.3 (𝜑𝐷 = 𝐵)
Assertion
Ref Expression
3sstr4d (𝜑𝐶𝐷)

Proof of Theorem 3sstr4d
StepHypRef Expression
1 3sstr4d.1 . 2 (𝜑𝐴𝐵)
2 3sstr4d.2 . . 3 (𝜑𝐶 = 𝐴)
3 3sstr4d.3 . . 3 (𝜑𝐷 = 𝐵)
42, 3sseq12d 3053 . 2 (𝜑 → (𝐶𝐷𝐴𝐵))
51, 4mpbird 165 1 (𝜑𝐶𝐷)
Colors of variables: wff set class
Syntax hints:  wi 4   = wceq 1289  wss 2997
This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 104  ax-ia2 105  ax-ia3 106  ax-5 1381  ax-7 1382  ax-gen 1383  ax-ie1 1427  ax-ie2 1428  ax-8 1440  ax-11 1442  ax-4 1445  ax-17 1464  ax-i9 1468  ax-ial 1472  ax-i5r 1473  ax-ext 2070
This theorem depends on definitions:  df-bi 115  df-nf 1395  df-sb 1693  df-clab 2075  df-cleq 2081  df-clel 2084  df-in 3003  df-ss 3010
This theorem is referenced by:  rdgss  6130  sucinc2  6189  oawordi  6212  nnnninf  6785  fzoss1  9547  fzoss2  9548  nnsf  11552  nninfself  11562
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