Definition df-subrg 20542

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 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 ∈ 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 20541	. 2 class SubRing
2		vw	. . 3 setvar 𝑤
3		crg 20205	. . 3 class Ring
4	2	cv 1546	. . . . . . 7 class 𝑤
5		vs	. . . . . . . 8 setvar 𝑠
6	5	cv 1546	. . . . . . 7 class 𝑠
7		cress 17191	. . . . . . 7 class ↾s
8	4, 6, 7	co 7356	. . . . . 6 class (𝑤 ↾s 𝑠)
9	8, 3	wcel 2119	. . . . 5 wff (𝑤 ↾s 𝑠) ∈ Ring
10		cur 20153	. . . . . . 7 class 1r
11	4, 10	cfv 6485	. . . . . 6 class (1r‘𝑤)
12	11, 6	wcel 2119	. . . . 5 wff (1r‘𝑤) ∈ 𝑠
13	9, 12	wa 396	. . . 4 wff ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)
14		cbs 17170	. . . . . 6 class Base
15	4, 14	cfv 6485	. . . . 5 class (Base‘𝑤)
16	15	cpw 4529	. . . 4 class 𝒫 (Base‘𝑤)
17	13, 5, 16	crab 3391	. . 3 class {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)}
18	2, 3, 17	cmpt 5153	. 2 class (𝑤 ∈ Ring ↦ {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)})
19	1, 18	wceq 1547	1 wff SubRing = (𝑤 ∈ Ring ↦ {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)})

This definition is referenced by:  issubrg  20543