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Theorem ssdifss 3099
 Description: Preservation of a subclass relationship by class difference. (Contributed by NM, 15-Feb-2007.)
Assertion
Ref Expression
ssdifss (𝐴𝐵 → (𝐴𝐶) ⊆ 𝐵)

Proof of Theorem ssdifss
StepHypRef Expression
1 difss 3095 . 2 (𝐴𝐶) ⊆ 𝐴
2 sstr 2978 . 2 (((𝐴𝐶) ⊆ 𝐴𝐴𝐵) → (𝐴𝐶) ⊆ 𝐵)
31, 2mpan 408 1 (𝐴𝐵 → (𝐴𝐶) ⊆ 𝐵)
 Colors of variables: wff set class Syntax hints:   → wi 4   ∖ cdif 2939   ⊆ wss 2942 This theorem was proved from axioms:  ax-1 5  ax-2 6  ax-mp 7  ax-ia1 103  ax-ia2 104  ax-ia3 105  ax-in1 552  ax-in2 553  ax-io 638  ax-5 1350  ax-7 1351  ax-gen 1352  ax-ie1 1396  ax-ie2 1397  ax-8 1409  ax-10 1410  ax-11 1411  ax-i12 1412  ax-bndl 1413  ax-4 1414  ax-17 1433  ax-i9 1437  ax-ial 1441  ax-i5r 1442  ax-ext 2036 This theorem depends on definitions:  df-bi 114  df-tru 1260  df-nf 1364  df-sb 1660  df-clab 2041  df-cleq 2047  df-clel 2050  df-nfc 2181  df-v 2574  df-dif 2945  df-in 2949  df-ss 2956 This theorem is referenced by:  ssdifssd  3106
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