Theorem ssundif 4052

Description: A condition equivalent to inclusion in the union of two classes. (Contributed by NM, 26-Mar-2007.)

Assertion

Ref	Expression
ssundif	|- ( A C_ ( B u. C ) <-> ( A \ B ) C_ C )

Proof of Theorem ssundif

Dummy variable x is distinct from all other variables.

Step	Hyp	Ref	Expression
1		pm5.6 951	. . . 4 |- ( ( ( x e. A /\ -. x e. B ) -> x e. C ) <-> ( x e. A -> ( x e. B \/ x e. C ) ) )
2		eldif 3584	. . . . 5 |- ( x e. ( A \ B ) <-> ( x e. A /\ -. x e. B ) )
3	2	imbi1i 339	. . . 4 |- ( ( x e. ( A \ B ) -> x e. C ) <-> ( ( x e. A /\ -. x e. B ) -> x e. C ) )
4		elun 3753	. . . . 5 |- ( x e. ( B u. C ) <-> ( x e. B \/ x e. C ) )
5	4	imbi2i 326	. . . 4 |- ( ( x e. A -> x e. ( B u. C ) ) <-> ( x e. A -> ( x e. B \/ x e. C ) ) )
6	1, 3, 5	3bitr4ri 293	. . 3 |- ( ( x e. A -> x e. ( B u. C ) ) <-> ( x e. ( A \ B ) -> x e. C ) )
7	6	albii 1747	. 2 |- ( A. x ( x e. A -> x e. ( B u. C ) ) <-> A. x ( x e. ( A \ B ) -> x e. C ) )
8		dfss2 3591	. 2 |- ( A C_ ( B u. C ) <-> A. x ( x e. A -> x e. ( B u. C ) ) )
9		dfss2 3591	. 2 |- ( ( A \ B ) C_ C <-> A. x ( x e. ( A \ B ) -> x e. C ) )
10	7, 8, 9	3bitr4i 292	1 |- ( A C_ ( B u. C ) <-> ( A \ B ) C_ C )

Syntax hints:   -. wn 3   -> wi 4   <-> wb 196   \/ wo 383   /\ wa 384   A.wal 1481   e. wcel 1990   \ cdif 3571   u. cun 3572   C_ wss 3574

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-3 8  ax-gen 1722  ax-4 1737  ax-5 1839  ax-6 1888  ax-7 1935  ax-9 1999  ax-10 2019  ax-11 2034  ax-12 2047  ax-13 2246  ax-ext 2602

This theorem depends on definitions:  df-bi 197  df-or 385  df-an 386  df-tru 1486  df-ex 1705  df-nf 1710  df-sb 1881  df-clab 2609  df-cleq 2615  df-clel 2618  df-nfc 2753  df-v 3202  df-dif 3577  df-un 3579  df-in 3581  df-ss 3588

This theorem is referenced by:  difcom  4053  uneqdifeq  4057  uneqdifeqOLD  4058  ssunsn2  4359  elpwun  6977  soex  7109  ressuppssdif  7316  frfi  8205  cantnfp1lem3  8577  dfacfin7  9221  zornn0g  9327  fpwwe2lem13  9464  hashbclem  13236  incexclem  14568  ramub1lem1  15730  lpcls  21168  cmpcld  21205  alexsubALTlem3  21853  restmetu  22375  uniiccdif  23346  abelthlem2  24186  abelthlem3  24187  imadifss  33384  frege124d  38053