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Definition df-subrg 13533
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) ∣ ((𝑤s 𝑠) ∈ Ring ∧ (1r𝑤) ∈ 𝑠)})
Distinct variable group:   𝑤,𝑠

Detailed syntax breakdown of Definition df-subrg
StepHypRef Expression
1 csubrg 13531 . 2 class SubRing
2 vw . . 3 setvar 𝑤
3 crg 13317 . . 3 class Ring
42cv 1363 . . . . . . 7 class 𝑤
5 vs . . . . . . . 8 setvar 𝑠
65cv 1363 . . . . . . 7 class 𝑠
7 cress 12487 . . . . . . 7 class s
84, 6, 7co 5891 . . . . . 6 class (𝑤s 𝑠)
98, 3wcel 2160 . . . . 5 wff (𝑤s 𝑠) ∈ Ring
10 cur 13280 . . . . . . 7 class 1r
114, 10cfv 5231 . . . . . 6 class (1r𝑤)
1211, 6wcel 2160 . . . . 5 wff (1r𝑤) ∈ 𝑠
139, 12wa 104 . . . 4 wff ((𝑤s 𝑠) ∈ Ring ∧ (1r𝑤) ∈ 𝑠)
14 cbs 12486 . . . . . 6 class Base
154, 14cfv 5231 . . . . 5 class (Base‘𝑤)
1615cpw 3590 . . . 4 class 𝒫 (Base‘𝑤)
1713, 5, 16crab 2472 . . 3 class {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤s 𝑠) ∈ Ring ∧ (1r𝑤) ∈ 𝑠)}
182, 3, 17cmpt 4079 . 2 class (𝑤 ∈ Ring ↦ {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤s 𝑠) ∈ Ring ∧ (1r𝑤) ∈ 𝑠)})
191, 18wceq 1364 1 wff SubRing = (𝑤 ∈ Ring ↦ {𝑠 ∈ 𝒫 (Base‘𝑤) ∣ ((𝑤s 𝑠) ∈ Ring ∧ (1r𝑤) ∈ 𝑠)})
Colors of variables: wff set class
This definition is referenced by:  issubrg  13535
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