Theorem ssdif2d 3111

Description: If A is contained in B and C is contained in D, then ( A \ D ) is contained in ( B \ C ). Deduction form. (Contributed by David Moews, 1-May-2017.)

Hypotheses

Ref	Expression
ssdifd.1	|- ( ph -> A C_ B )
ssdif2d.2	|- ( ph -> C C_ D )

Assertion

Ref	Expression
ssdif2d	|- ( ph -> ( A \ D ) C_ ( B \ C ) )

Proof of Theorem ssdif2d

Step	Hyp	Ref	Expression
1		ssdif2d.2	. . 3 |- ( ph -> C C_ D )
2	1	sscond 3109	. 2 |- ( ph -> ( A \ D ) C_ ( A \ C ) )
3		ssdifd.1	. . 3 |- ( ph -> A C_ B )
4	3	ssdifd 3108	. 2 |- ( ph -> ( A \ C ) C_ ( B \ C ) )
5	2, 4	sstrd 3009	1 |- ( ph -> ( A \ D ) C_ ( B \ C ) )

Syntax hints:   -> wi 4   \ cdif 2970   C_ wss 2973

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-in1 576  ax-in2 577  ax-io 662  ax-5 1376  ax-7 1377  ax-gen 1378  ax-ie1 1422  ax-ie2 1423  ax-8 1435  ax-10 1436  ax-11 1437  ax-i12 1438  ax-bndl 1439  ax-4 1440  ax-17 1459  ax-i9 1463  ax-ial 1467  ax-i5r 1468  ax-ext 2063

This theorem depends on definitions:  df-bi 115  df-tru 1287  df-nf 1390  df-sb 1686  df-clab 2068  df-cleq 2074  df-clel 2077  df-nfc 2208  df-v 2603  df-dif 2975  df-in 2979  df-ss 2986

This theorem is referenced by: (None)