Definition df-subrg 13981

Description: Define a subring of a ring as a set of elements that is a ring in its own right and contains the multiplicative identity.

The additional constraint is necessary because the multiplicative identity of a ring, unlike the additive identity of a ring/group or the multiplicative identity of a field, cannot be identified by a local property. Thus, it is possible for a subset of a ring to be a ring while not containing the true identity if it contains a false identity. For instance, the subset ( ZZ X. { 0 } ) of ( ZZ X. ZZ ) (where multiplication is componentwise) contains the false identity <. 1 , 0 >. which preserves every element of the subset and thus appears to be the identity of the subset, but is not the identity of the larger ring. (Contributed by Stefan O'Rear, 27-Nov-2014.)

Assertion

Ref	Expression
df-subrg	|- SubRing = ( w e. Ring |-> { s e. ~P ( Base ` w ) | ( ( w ↾s s ) e. Ring /\ ( 1r ` w ) e. s ) } )

Distinct variable group:   w, s

Detailed syntax breakdown of Definition df-subrg

Step	Hyp	Ref	Expression
1		csubrg 13979	. 2 class SubRing
2		vw	. . 3 setvar w
3		crg 13758	. . 3 class Ring
4	2	cv 1372	. . . . . . 7 class w
5		vs	. . . . . . . 8 setvar s
6	5	cv 1372	. . . . . . 7 class s
7		cress 12833	. . . . . . 7 class ↾s
8	4, 6, 7	co 5944	. . . . . 6 class ( w ↾s s )
9	8, 3	wcel 2176	. . . . 5 wff ( w ↾s s ) e. Ring
10		cur 13721	. . . . . . 7 class 1r
11	4, 10	cfv 5271	. . . . . 6 class ( 1r ` w )
12	11, 6	wcel 2176	. . . . 5 wff ( 1r ` w ) e. s
13	9, 12	wa 104	. . . 4 wff ( ( w ↾s s ) e. Ring /\ ( 1r ` w ) e. s )
14		cbs 12832	. . . . . 6 class Base
15	4, 14	cfv 5271	. . . . 5 class ( Base ` w )
16	15	cpw 3616	. . . 4 class ~P ( Base ` w )
17	13, 5, 16	crab 2488	. . 3 class { s e. ~P ( Base ` w ) | ( ( w ↾s s ) e. Ring /\ ( 1r ` w ) e. s ) }
18	2, 3, 17	cmpt 4105	. 2 class ( w e. Ring |-> { s e. ~P ( Base ` w ) | ( ( w ↾s s ) e. Ring /\ ( 1r ` w ) e. s ) } )
19	1, 18	wceq 1373	1 wff SubRing = ( w e. Ring |-> { s e. ~P ( Base ` w ) | ( ( w ↾s s ) e. Ring /\ ( 1r ` w ) e. s ) } )

This definition is referenced by:  issubrg  13983