Theorem ssint 3970

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 3230	. 2 |- ( A C_ |^| B <-> A. y e. A y e. |^| B )
2		vex 2818	. . . 4 |- y e. _V
3	2	elint2 3961	. . 3 |- ( y e. |^| B <-> A. x e. B y e. x )
4	3	ralbii 2550	. 2 |- ( A. y e. A y e. |^| B <-> A. y e. A A. x e. B y e. x )
5		ralcom 2708	. . 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 3230	. . . 4 |- ( A C_ x <-> A. y e. A y e. x )
7	6	ralbii 2550	. . 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 2205   A.wral 2522   C_ wss 3214   |^|cint 3954

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 717  ax-5 1496  ax-7 1497  ax-gen 1498  ax-ie1 1542  ax-ie2 1543  ax-8 1553  ax-10 1554  ax-11 1555  ax-i12 1556  ax-bndl 1558  ax-4 1559  ax-17 1575  ax-i9 1579  ax-ial 1583  ax-i5r 1584  ax-ext 2216

This theorem depends on definitions:  df-bi 117  df-tru 1401  df-nf 1510  df-sb 1812  df-clab 2221  df-cleq 2227  df-clel 2230  df-nfc 2375  df-ral 2527  df-v 2817  df-in 3220  df-ss 3227  df-int 3955

This theorem is referenced by:  ssintab  3971  ssintub  3972  iinpw  4087  trint  4228  fintm  5557  bj-ssom  16832