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Theorem ssdif 3262
Description: Difference law for subsets. (Contributed by NM, 28-May-1998.)
Assertion
Ref Expression
ssdif  |-  ( A 
C_  B  ->  ( A  \  C )  C_  ( B  \  C ) )

Proof of Theorem ssdif
Dummy variable  x is distinct from all other variables.
StepHypRef Expression
1 ssel 3141 . . . 4  |-  ( A 
C_  B  ->  (
x  e.  A  ->  x  e.  B )
)
21anim1d 334 . . 3  |-  ( A 
C_  B  ->  (
( x  e.  A  /\  -.  x  e.  C
)  ->  ( x  e.  B  /\  -.  x  e.  C ) ) )
3 eldif 3130 . . 3  |-  ( x  e.  ( A  \  C )  <->  ( x  e.  A  /\  -.  x  e.  C ) )
4 eldif 3130 . . 3  |-  ( x  e.  ( B  \  C )  <->  ( x  e.  B  /\  -.  x  e.  C ) )
52, 3, 43imtr4g 204 . 2  |-  ( A 
C_  B  ->  (
x  e.  ( A 
\  C )  ->  x  e.  ( B  \  C ) ) )
65ssrdv 3153 1  |-  ( A 
C_  B  ->  ( A  \  C )  C_  ( B  \  C ) )
Colors of variables: wff set class
Syntax hints:   -. wn 3    -> wi 4    /\ wa 103    e. wcel 2141    \ cdif 3118    C_ wss 3121
This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 105  ax-ia2 106  ax-ia3 107  ax-in1 609  ax-in2 610  ax-io 704  ax-5 1440  ax-7 1441  ax-gen 1442  ax-ie1 1486  ax-ie2 1487  ax-8 1497  ax-10 1498  ax-11 1499  ax-i12 1500  ax-bndl 1502  ax-4 1503  ax-17 1519  ax-i9 1523  ax-ial 1527  ax-i5r 1528  ax-ext 2152
This theorem depends on definitions:  df-bi 116  df-tru 1351  df-nf 1454  df-sb 1756  df-clab 2157  df-cleq 2163  df-clel 2166  df-nfc 2301  df-v 2732  df-dif 3123  df-in 3127  df-ss 3134
This theorem is referenced by:  ssdifd  3263  phpm  6843  difinfinf  7078
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