Theorem ssint 3938

Description: Subclass of a class intersection. Theorem 5.11(viii) of [Monk1] p. 52 and its converse. (Contributed by NM, 14-Oct-1999.)

Assertion

Ref	Expression
ssint	|- ( A C_ |^| B <-> A. x e. B A C_ x )

Distinct variable groups:   x, A   x, B

Proof of Theorem ssint

Dummy variable y is distinct from all other variables.

Step	Hyp	Ref	Expression
1		dfss3 3213	. 2 |- ( A C_ |^| B <-> A. y e. A y e. |^| B )
2		vex 2802	. . . 4 |- y e. _V
3	2	elint2 3929	. . 3 |- ( y e. |^| B <-> A. x e. B y e. x )
4	3	ralbii 2536	. 2 |- ( A. y e. A y e. |^| B <-> A. y e. A A. x e. B y e. x )
5		ralcom 2694	. . 3 |- ( A. y e. A A. x e. B y e. x <-> A. x e. B A. y e. A y e. x )
6		dfss3 3213	. . . 4 |- ( A C_ x <-> A. y e. A y e. x )
7	6	ralbii 2536	. . 3 |- ( A. x e. B A C_ x <-> A. x e. B A. y e. A y e. x )
8	5, 7	bitr4i 187	. 2 |- ( A. y e. A A. x e. B y e. x <-> A. x e. B A C_ x )
9	1, 4, 8	3bitri 206	1 |- ( A C_ |^| B <-> A. x e. B A C_ x )

Syntax hints:   <-> wb 105   e. wcel 2200   A.wral 2508   C_ wss 3197   |^|cint 3922

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-io 714  ax-5 1493  ax-7 1494  ax-gen 1495  ax-ie1 1539  ax-ie2 1540  ax-8 1550  ax-10 1551  ax-11 1552  ax-i12 1553  ax-bndl 1555  ax-4 1556  ax-17 1572  ax-i9 1576  ax-ial 1580  ax-i5r 1581  ax-ext 2211

This theorem depends on definitions:  df-bi 117  df-tru 1398  df-nf 1507  df-sb 1809  df-clab 2216  df-cleq 2222  df-clel 2225  df-nfc 2361  df-ral 2513  df-v 2801  df-in 3203  df-ss 3210  df-int 3923

This theorem is referenced by:  ssintab  3939  ssintub  3940  iinpw  4055  trint  4196  fintm  5510  bj-ssom  16257