Definition df-subrg 18601

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 (ℤ × {0}) of (ℤ × ℤ) (where multiplication is component-wise) 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 ∈ Ring ↦ {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)})

Distinct variable group:   𝑤,𝑠

Detailed syntax breakdown of Definition df-subrg

Step	Hyp	Ref	Expression
1		csubrg 18599	. 2 class SubRing
2		vw	. . 3 setvar 𝑤
3		crg 18370	. . 3 class Ring
4	2	cv 1474	. . . . . . 7 class 𝑤
5		vs	. . . . . . . 8 setvar 𝑠
6	5	cv 1474	. . . . . . 7 class 𝑠
7		cress 15696	. . . . . . 7 class ↾s
8	4, 6, 7	co 6549	. . . . . 6 class (𝑤 ↾s 𝑠)
9	8, 3	wcel 1977	. . . . 5 wff (𝑤 ↾s 𝑠) ∈ Ring
10		cur 18324	. . . . . . 7 class 1r
11	4, 10	cfv 5804	. . . . . 6 class (1r‘𝑤)
12	11, 6	wcel 1977	. . . . 5 wff (1r‘𝑤) ∈ 𝑠
13	9, 12	wa 383	. . . 4 wff ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)
14		cbs 15695	. . . . . 6 class Base
15	4, 14	cfv 5804	. . . . 5 class (Base‘𝑤)
16	15	cpw 4108	. . . 4 class 𝒫 (Base‘𝑤)
17	13, 5, 16	crab 2900	. . 3 class {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)}
18	2, 3, 17	cmpt 4643	. 2 class (𝑤 ∈ Ring ↦ {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)})
19	1, 18	wceq 1475	1 wff SubRing = (𝑤 ∈ Ring ↦ {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)})

This definition is referenced by:  issubrg  18603