Theorem ssint 3981

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 3236	. 2 |- ( A C_ |^| B <-> A. y e. A y e. |^| B )
2		vex 2824	. . . 4 |- y e. _V
3	2	elint2 3972	. . 3 |- ( y e. |^| B <-> A. x e. B y e. x )
4	3	ralbii 2556	. 2 |- ( A. y e. A y e. |^| B <-> A. y e. A A. x e. B y e. x )
5		ralcom 2714	. . 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 3236	. . . 4 |- ( A C_ x <-> A. y e. A y e. x )
7	6	ralbii 2556	. . 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 2209   A.wral 2528   C_ wss 3220   |^|cint 3965

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 721  ax-5 1500  ax-7 1501  ax-gen 1502  ax-ie1 1546  ax-ie2 1547  ax-8 1557  ax-10 1558  ax-11 1559  ax-i12 1560  ax-bndl 1562  ax-4 1563  ax-17 1579  ax-i9 1583  ax-ial 1587  ax-i5r 1588  ax-ext 2220

This theorem depends on definitions:  df-bi 117  df-tru 1405  df-nf 1514  df-sb 1816  df-clab 2225  df-cleq 2231  df-clel 2234  df-nfc 2381  df-ral 2533  df-v 2823  df-in 3226  df-ss 3233  df-int 3966

This theorem is referenced by:  ssintab  3982  ssintub  3983  iinpw  4098  trint  4239  fintm  5572  bj-ssom  16876