Definition df-subrg 20528

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 20527	. 2 class SubRing
2		vw	. . 3 setvar 𝑤
3		crg 20191	. . 3 class Ring
4	2	cv 1539	. . . . . . 7 class 𝑤
5		vs	. . . . . . . 8 setvar 𝑠
6	5	cv 1539	. . . . . . 7 class 𝑠
7		cress 17249	. . . . . . 7 class ↾s
8	4, 6, 7	co 7403	. . . . . 6 class (𝑤 ↾s 𝑠)
9	8, 3	wcel 2108	. . . . 5 wff (𝑤 ↾s 𝑠) ∈ Ring
10		cur 20139	. . . . . . 7 class 1r
11	4, 10	cfv 6530	. . . . . 6 class (1r‘𝑤)
12	11, 6	wcel 2108	. . . . 5 wff (1r‘𝑤) ∈ 𝑠
13	9, 12	wa 395	. . . 4 wff ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)
14		cbs 17226	. . . . . 6 class Base
15	4, 14	cfv 6530	. . . . 5 class (Base‘𝑤)
16	15	cpw 4575	. . . 4 class 𝒫 (Base‘𝑤)
17	13, 5, 16	crab 3415	. . 3 class {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)}
18	2, 3, 17	cmpt 5201	. 2 class (𝑤 ∈ Ring ↦ {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)})
19	1, 18	wceq 1540	1 wff SubRing = (𝑤 ∈ Ring ↦ {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤 ↾s 𝑠) ∈ Ring ∧ (1r‘𝑤) ∈ 𝑠)})

This definition is referenced by:  issubrg  20529