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Theorem sscond 3272
Description: If  A is contained in  B, then  ( C  \  B ) is contained in  ( C  \  A ). Deduction form of sscon 3269. (Contributed by David Moews, 1-May-2017.)
Hypothesis
Ref Expression
ssdifd.1  |-  ( ph  ->  A  C_  B )
Assertion
Ref Expression
sscond  |-  ( ph  ->  ( C  \  B
)  C_  ( C  \  A ) )

Proof of Theorem sscond
StepHypRef Expression
1 ssdifd.1 . 2  |-  ( ph  ->  A  C_  B )
2 sscon 3269 . 2  |-  ( A 
C_  B  ->  ( C  \  B )  C_  ( C  \  A ) )
31, 2syl 14 1  |-  ( ph  ->  ( C  \  B
)  C_  ( C  \  A ) )
Colors of variables: wff set class
Syntax hints:    -> wi 4    \ cdif 3126    C_ wss 3129
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-in1 614  ax-in2 615  ax-io 709  ax-5 1447  ax-7 1448  ax-gen 1449  ax-ie1 1493  ax-ie2 1494  ax-8 1504  ax-10 1505  ax-11 1506  ax-i12 1507  ax-bndl 1509  ax-4 1510  ax-17 1526  ax-i9 1530  ax-ial 1534  ax-i5r 1535  ax-ext 2159
This theorem depends on definitions:  df-bi 117  df-tru 1356  df-nf 1461  df-sb 1763  df-clab 2164  df-cleq 2170  df-clel 2173  df-nfc 2308  df-v 2739  df-dif 3131  df-in 3135  df-ss 3142
This theorem is referenced by:  ssdif2d  3274  setsresg  12470
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