P. 369 of Theorem List - Metamath Proof Explorer

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**Theorem List for Metamath Proof Explorer -** 36801-36900 *Has distinct variable group(s)
Type	Label	Description
Statement

Theorem	rngorn1 36801	In a unital ring the range of the addition equals the domain of the first variable of the multiplication. (Contributed by FL, 24-Jan-2010.) (New usage is discouraged.)
⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝐺 = (1^st ‘𝑅) ⇒ ⊢ (𝑅 ∈ RingOps → ran 𝐺 = dom dom 𝐻)

Theorem	rngorn1eq 36802	In a unital ring the range of the addition equals the range of the multiplication. (Contributed by FL, 24-Jan-2010.) (New usage is discouraged.)
⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝐺 = (1^st ‘𝑅) ⇒ ⊢ (𝑅 ∈ RingOps → ran 𝐺 = ran 𝐻)

Theorem	rngomndo 36803	In a unital ring the multiplication is a monoid. (Contributed by FL, 24-Jan-2010.) (Revised by Mario Carneiro, 22-Dec-2013.) (New usage is discouraged.)
⊢ 𝐻 = (2^nd ‘𝑅) ⇒ ⊢ (𝑅 ∈ RingOps → 𝐻 ∈ MndOp)

Theorem	rngoidmlem 36804	The unity element of a ring is an identity element for the multiplication. (Contributed by FL, 18-Feb-2010.) (New usage is discouraged.)
⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran (1^st ‘𝑅) & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐴 ∈ 𝑋) → ((𝑈𝐻𝐴) = 𝐴 ∧ (𝐴𝐻𝑈) = 𝐴))

Theorem	rngolidm 36805	The unity element of a ring is an identity element for the multiplication. (Contributed by FL, 18-Apr-2010.) (New usage is discouraged.)
⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran (1^st ‘𝑅) & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐴 ∈ 𝑋) → (𝑈𝐻𝐴) = 𝐴)

Theorem	rngoridm 36806	The unity element of a ring is an identity element for the multiplication. (Contributed by FL, 18-Apr-2010.) (New usage is discouraged.)
⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran (1^st ‘𝑅) & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐴 ∈ 𝑋) → (𝐴𝐻𝑈) = 𝐴)

Theorem	rngo1cl 36807	The unity element of a ring belongs to the base set. (Contributed by FL, 12-Feb-2010.) (New usage is discouraged.)
⊢ 𝑋 = ran (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ (𝑅 ∈ RingOps → 𝑈 ∈ 𝑋)

Theorem	rngoueqz 36808	Obsolete as of 23-Jan-2020. Use 0ring01eqbi 20307 instead. In a unital ring the zero equals the ring unity iff the ring is the zero ring. (Contributed by FL, 14-Feb-2010.) (New usage is discouraged.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑍 = (GId‘𝐺) & ⊢ 𝑈 = (GId‘𝐻) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ (𝑅 ∈ RingOps → (𝑋 ≈ 1_o ↔ 𝑈 = 𝑍))

Theorem	rngonegmn1l 36809	Negation in a ring is the same as left multiplication by -1. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑁 = (inv‘𝐺) & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐴 ∈ 𝑋) → (𝑁‘𝐴) = ((𝑁‘𝑈)𝐻𝐴))

Theorem	rngonegmn1r 36810	Negation in a ring is the same as right multiplication by -1. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑁 = (inv‘𝐺) & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐴 ∈ 𝑋) → (𝑁‘𝐴) = (𝐴𝐻(𝑁‘𝑈)))

Theorem	rngoneglmul 36811	Negation of a product in a ring. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑁 = (inv‘𝐺) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) → (𝑁‘(𝐴𝐻𝐵)) = ((𝑁‘𝐴)𝐻𝐵))

Theorem	rngonegrmul 36812	Negation of a product in a ring. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑁 = (inv‘𝐺) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) → (𝑁‘(𝐴𝐻𝐵)) = (𝐴𝐻(𝑁‘𝐵)))

Theorem	rngosubdi 36813	Ring multiplication distributes over subtraction. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐷 = ( /_𝑔 ‘𝐺) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ (𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ 𝐶 ∈ 𝑋)) → (𝐴𝐻(𝐵𝐷𝐶)) = ((𝐴𝐻𝐵)𝐷(𝐴𝐻𝐶)))

Theorem	rngosubdir 36814	Ring multiplication distributes over subtraction. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐷 = ( /_𝑔 ‘𝐺) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ (𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ 𝐶 ∈ 𝑋)) → ((𝐴𝐷𝐵)𝐻𝐶) = ((𝐴𝐻𝐶)𝐷(𝐵𝐻𝐶)))

Theorem	zerdivemp1x 36815*	In a unital ring a left invertible element is not a zero divisor. See also ringinvnzdiv 20113. (Contributed by Jeff Madsen, 18-Apr-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑍 = (GId‘𝐺) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐴 ∈ 𝑋 ∧ ∃𝑎 ∈ 𝑋 (𝑎𝐻𝐴) = 𝑈) → (𝐵 ∈ 𝑋 → ((𝐴𝐻𝐵) = 𝑍 → 𝐵 = 𝑍)))

21.22.17 Division Rings

Syntax	cdrng 36816	Extend class notation with the class of all division rings.
class DivRingOps

Definition	df-drngo 36817*	Define the class of all division rings (sometimes called skew fields). A division ring is a unital ring where every element except the additive identity has a multiplicative inverse. (Contributed by NM, 4-Apr-2009.) (New usage is discouraged.)
⊢ DivRingOps = {⟨𝑔, ℎ⟩ ∣ (⟨𝑔, ℎ⟩ ∈ RingOps ∧ (ℎ ↾ ((ran 𝑔 ∖ {(GId‘𝑔)}) × (ran 𝑔 ∖ {(GId‘𝑔)}))) ∈ GrpOp)}

Theorem	isdivrngo 36818	The predicate "is a division ring". (Contributed by FL, 6-Sep-2009.) (New usage is discouraged.)
⊢ (𝐻 ∈ 𝐴 → (⟨𝐺, 𝐻⟩ ∈ DivRingOps ↔ (⟨𝐺, 𝐻⟩ ∈ RingOps ∧ (𝐻 ↾ ((ran 𝐺 ∖ {(GId‘𝐺)}) × (ran 𝐺 ∖ {(GId‘𝐺)}))) ∈ GrpOp)))

Theorem	drngoi 36819	The properties of a division ring. (Contributed by NM, 4-Apr-2009.) (New usage is discouraged.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑍 = (GId‘𝐺) ⇒ ⊢ (𝑅 ∈ DivRingOps → (𝑅 ∈ RingOps ∧ (𝐻 ↾ ((𝑋 ∖ {𝑍}) × (𝑋 ∖ {𝑍}))) ∈ GrpOp))

Theorem	gidsn 36820	Obsolete as of 23-Jan-2020. Use mnd1id 18668 instead. The identity element of the trivial group. (Contributed by FL, 21-Jun-2010.) (Proof shortened by Mario Carneiro, 15-Dec-2013.) (New usage is discouraged.)
⊢ 𝐴 ∈ V ⇒ ⊢ (GId‘{⟨⟨𝐴, 𝐴⟩, 𝐴⟩}) = 𝐴

Theorem	zrdivrng 36821	The zero ring is not a division ring. (Contributed by FL, 24-Jan-2010.) (Proof shortened by Mario Carneiro, 15-Dec-2013.) (New usage is discouraged.)
⊢ 𝐴 ∈ V ⇒ ⊢ ¬ ⟨{⟨⟨𝐴, 𝐴⟩, 𝐴⟩}, {⟨⟨𝐴, 𝐴⟩, 𝐴⟩}⟩ ∈ DivRingOps

Theorem	dvrunz 36822	In a division ring the ring unit is different from the zero. (Contributed by FL, 14-Feb-2010.) (Revised by Mario Carneiro, 15-Dec-2013.) (New usage is discouraged.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑍 = (GId‘𝐺) & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ (𝑅 ∈ DivRingOps → 𝑈 ≠ 𝑍)

Theorem	isgrpda 36823*	Properties that determine a group operation. (Contributed by Jeff Madsen, 1-Dec-2009.) (New usage is discouraged.)
⊢ (𝜑 → 𝑋 ∈ V) & ⊢ (𝜑 → 𝐺:(𝑋 × 𝑋)⟶𝑋) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝑋 ∧ 𝑦 ∈ 𝑋 ∧ 𝑧 ∈ 𝑋)) → ((𝑥𝐺𝑦)𝐺𝑧) = (𝑥𝐺(𝑦𝐺𝑧))) & ⊢ (𝜑 → 𝑈 ∈ 𝑋) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝑋) → (𝑈𝐺𝑥) = 𝑥) & ⊢ ((𝜑 ∧ 𝑥 ∈ 𝑋) → ∃𝑛 ∈ 𝑋 (𝑛𝐺𝑥) = 𝑈) ⇒ ⊢ (𝜑 → 𝐺 ∈ GrpOp)

Theorem	isdrngo1 36824	The predicate "is a division ring". (Contributed by Jeff Madsen, 8-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑍 = (GId‘𝐺) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ (𝑅 ∈ DivRingOps ↔ (𝑅 ∈ RingOps ∧ (𝐻 ↾ ((𝑋 ∖ {𝑍}) × (𝑋 ∖ {𝑍}))) ∈ GrpOp))

Theorem	divrngcl 36825	The product of two nonzero elements of a division ring is nonzero. (Contributed by Jeff Madsen, 9-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑍 = (GId‘𝐺) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ ((𝑅 ∈ DivRingOps ∧ 𝐴 ∈ (𝑋 ∖ {𝑍}) ∧ 𝐵 ∈ (𝑋 ∖ {𝑍})) → (𝐴𝐻𝐵) ∈ (𝑋 ∖ {𝑍}))

Theorem	isdrngo2 36826*	A division ring is a ring in which 1 ≠ 0 and every nonzero element is invertible. (Contributed by Jeff Madsen, 8-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑍 = (GId‘𝐺) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ (𝑅 ∈ DivRingOps ↔ (𝑅 ∈ RingOps ∧ (𝑈 ≠ 𝑍 ∧ ∀𝑥 ∈ (𝑋 ∖ {𝑍})∃𝑦 ∈ (𝑋 ∖ {𝑍})(𝑦𝐻𝑥) = 𝑈)))

Theorem	isdrngo3 36827*	A division ring is a ring in which 1 ≠ 0 and every nonzero element is invertible. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑍 = (GId‘𝐺) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ (𝑅 ∈ DivRingOps ↔ (𝑅 ∈ RingOps ∧ (𝑈 ≠ 𝑍 ∧ ∀𝑥 ∈ (𝑋 ∖ {𝑍})∃𝑦 ∈ 𝑋 (𝑦𝐻𝑥) = 𝑈)))

21.22.18 Ring homomorphisms

Syntax	crnghom 36828	Extend class notation with the class of ring homomorphisms.
class RngHom

Syntax	crngiso 36829	Extend class notation with the class of ring isomorphisms.
class RngIso

Syntax	crisc 36830	Extend class notation with the ring isomorphism relation.
class ≃_𝑟

Definition	df-rngohom 36831*	Define the function which gives the set of ring homomorphisms between two given rings. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ RngHom = (𝑟 ∈ RingOps, 𝑠 ∈ RingOps ↦ {𝑓 ∈ (ran (1^st ‘𝑠) ↑_m ran (1^st ‘𝑟)) ∣ ((𝑓‘(GId‘(2^nd ‘𝑟))) = (GId‘(2^nd ‘𝑠)) ∧ ∀𝑥 ∈ ran (1^st ‘𝑟)∀𝑦 ∈ ran (1^st ‘𝑟)((𝑓‘(𝑥(1^st ‘𝑟)𝑦)) = ((𝑓‘𝑥)(1^st ‘𝑠)(𝑓‘𝑦)) ∧ (𝑓‘(𝑥(2^nd ‘𝑟)𝑦)) = ((𝑓‘𝑥)(2^nd ‘𝑠)(𝑓‘𝑦))))})

Theorem	rngohomval 36832*	The set of ring homomorphisms. (Contributed by Jeff Madsen, 19-Jun-2010.) (Revised by Mario Carneiro, 22-Sep-2015.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑈 = (GId‘𝐻) & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝐾 = (2^nd ‘𝑆) & ⊢ 𝑌 = ran 𝐽 & ⊢ 𝑉 = (GId‘𝐾) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps) → (𝑅 RngHom 𝑆) = {𝑓 ∈ (𝑌 ↑_m 𝑋) ∣ ((𝑓‘𝑈) = 𝑉 ∧ ∀𝑥 ∈ 𝑋 ∀𝑦 ∈ 𝑋 ((𝑓‘(𝑥𝐺𝑦)) = ((𝑓‘𝑥)𝐽(𝑓‘𝑦)) ∧ (𝑓‘(𝑥𝐻𝑦)) = ((𝑓‘𝑥)𝐾(𝑓‘𝑦))))})

Theorem	isrngohom 36833*	The predicate "is a ring homomorphism from 𝑅 to 𝑆". (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑈 = (GId‘𝐻) & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝐾 = (2^nd ‘𝑆) & ⊢ 𝑌 = ran 𝐽 & ⊢ 𝑉 = (GId‘𝐾) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps) → (𝐹 ∈ (𝑅 RngHom 𝑆) ↔ (𝐹:𝑋⟶𝑌 ∧ (𝐹‘𝑈) = 𝑉 ∧ ∀𝑥 ∈ 𝑋 ∀𝑦 ∈ 𝑋 ((𝐹‘(𝑥𝐺𝑦)) = ((𝐹‘𝑥)𝐽(𝐹‘𝑦)) ∧ (𝐹‘(𝑥𝐻𝑦)) = ((𝐹‘𝑥)𝐾(𝐹‘𝑦))))))

Theorem	rngohomf 36834	A ring homomorphism is a function. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝑌 = ran 𝐽 ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) → 𝐹:𝑋⟶𝑌)

Theorem	rngohomcl 36835	Closure law for a ring homomorphism. (Contributed by Jeff Madsen, 3-Jan-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝑌 = ran 𝐽 ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) ∧ 𝐴 ∈ 𝑋) → (𝐹‘𝐴) ∈ 𝑌)

Theorem	rngohom1 36836	A ring homomorphism preserves 1. (Contributed by Jeff Madsen, 24-Jun-2011.)
⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑈 = (GId‘𝐻) & ⊢ 𝐾 = (2^nd ‘𝑆) & ⊢ 𝑉 = (GId‘𝐾) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) → (𝐹‘𝑈) = 𝑉)

Theorem	rngohomadd 36837	Ring homomorphisms preserve addition. (Contributed by Jeff Madsen, 3-Jan-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐽 = (1^st ‘𝑆) ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) ∧ (𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋)) → (𝐹‘(𝐴𝐺𝐵)) = ((𝐹‘𝐴)𝐽(𝐹‘𝐵)))

Theorem	rngohommul 36838	Ring homomorphisms preserve multiplication. (Contributed by Jeff Madsen, 3-Jan-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝐾 = (2^nd ‘𝑆) ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) ∧ (𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋)) → (𝐹‘(𝐴𝐻𝐵)) = ((𝐹‘𝐴)𝐾(𝐹‘𝐵)))

Theorem	rngogrphom 36839	A ring homomorphism is a group homomorphism. (Contributed by Jeff Madsen, 2-Jan-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐽 = (1^st ‘𝑆) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) → 𝐹 ∈ (𝐺 GrpOpHom 𝐽))

Theorem	rngohom0 36840	A ring homomorphism preserves 0. (Contributed by Jeff Madsen, 2-Jan-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑍 = (GId‘𝐺) & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝑊 = (GId‘𝐽) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) → (𝐹‘𝑍) = 𝑊)

Theorem	rngohomsub 36841	Ring homomorphisms preserve subtraction. (Contributed by Jeff Madsen, 15-Jun-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐻 = ( /_𝑔 ‘𝐺) & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝐾 = ( /_𝑔 ‘𝐽) ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) ∧ (𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋)) → (𝐹‘(𝐴𝐻𝐵)) = ((𝐹‘𝐴)𝐾(𝐹‘𝐵)))

Theorem	rngohomco 36842	The composition of two ring homomorphisms is a ring homomorphism. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ (((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝑇 ∈ RingOps) ∧ (𝐹 ∈ (𝑅 RngHom 𝑆) ∧ 𝐺 ∈ (𝑆 RngHom 𝑇))) → (𝐺 ∘ 𝐹) ∈ (𝑅 RngHom 𝑇))

Theorem	rngokerinj 36843	A ring homomorphism is injective if and only if its kernel is zero. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑊 = (GId‘𝐺) & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝑌 = ran 𝐽 & ⊢ 𝑍 = (GId‘𝐽) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) → (𝐹:𝑋–1-1→𝑌 ↔ (^◡𝐹 “ {𝑍}) = {𝑊}))

Definition	df-rngoiso 36844*	Define the function which gives the set of ring isomorphisms between two given rings. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ RngIso = (𝑟 ∈ RingOps, 𝑠 ∈ RingOps ↦ {𝑓 ∈ (𝑟 RngHom 𝑠) ∣ 𝑓:ran (1^st ‘𝑟)–1-1-onto→ran (1^st ‘𝑠)})

Theorem	rngoisoval 36845*	The set of ring isomorphisms. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝑌 = ran 𝐽 ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps) → (𝑅 RngIso 𝑆) = {𝑓 ∈ (𝑅 RngHom 𝑆) ∣ 𝑓:𝑋–1-1-onto→𝑌})

Theorem	isrngoiso 36846	The predicate "is a ring isomorphism between 𝑅 and 𝑆". (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝑌 = ran 𝐽 ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps) → (𝐹 ∈ (𝑅 RngIso 𝑆) ↔ (𝐹 ∈ (𝑅 RngHom 𝑆) ∧ 𝐹:𝑋–1-1-onto→𝑌)))

Theorem	rngoiso1o 36847	A ring isomorphism is a bijection. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝑌 = ran 𝐽 ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngIso 𝑆)) → 𝐹:𝑋–1-1-onto→𝑌)

Theorem	rngoisohom 36848	A ring isomorphism is a ring homomorphism. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngIso 𝑆)) → 𝐹 ∈ (𝑅 RngHom 𝑆))

Theorem	rngoisocnv 36849	The inverse of a ring isomorphism is a ring isomorphism. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngIso 𝑆)) → ^◡𝐹 ∈ (𝑆 RngIso 𝑅))

Theorem	rngoisoco 36850	The composition of two ring isomorphisms is a ring isomorphism. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ (((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝑇 ∈ RingOps) ∧ (𝐹 ∈ (𝑅 RngIso 𝑆) ∧ 𝐺 ∈ (𝑆 RngIso 𝑇))) → (𝐺 ∘ 𝐹) ∈ (𝑅 RngIso 𝑇))

Definition	df-risc 36851*	Define the ring isomorphism relation. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ ≃_𝑟 = {⟨𝑟, 𝑠⟩ ∣ ((𝑟 ∈ RingOps ∧ 𝑠 ∈ RingOps) ∧ ∃𝑓 𝑓 ∈ (𝑟 RngIso 𝑠))}

Theorem	isriscg 36852*	The ring isomorphism relation. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ ((𝑅 ∈ 𝐴 ∧ 𝑆 ∈ 𝐵) → (𝑅 ≃_𝑟 𝑆 ↔ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps) ∧ ∃𝑓 𝑓 ∈ (𝑅 RngIso 𝑆))))

Theorem	isrisc 36853*	The ring isomorphism relation. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ 𝑅 ∈ V & ⊢ 𝑆 ∈ V ⇒ ⊢ (𝑅 ≃_𝑟 𝑆 ↔ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps) ∧ ∃𝑓 𝑓 ∈ (𝑅 RngIso 𝑆)))

Theorem	risc 36854*	The ring isomorphism relation. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps) → (𝑅 ≃_𝑟 𝑆 ↔ ∃𝑓 𝑓 ∈ (𝑅 RngIso 𝑆)))

Theorem	risci 36855	Determine that two rings are isomorphic. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngIso 𝑆)) → 𝑅 ≃_𝑟 𝑆)

Theorem	riscer 36856	Ring isomorphism is an equivalence relation. (Contributed by Jeff Madsen, 16-Jun-2011.) (Revised by Mario Carneiro, 12-Aug-2015.)
⊢ ≃_𝑟 Er dom ≃_𝑟

21.22.19 Commutative rings

Syntax	ccm2 36857	Extend class notation with a class that adds commutativity to various flavors of rings.
class Com2

Definition	df-com2 36858*	A device to add commutativity to various sorts of rings. I use ran 𝑔 because I suppose 𝑔 has a neutral element and therefore is onto. (Contributed by FL, 6-Sep-2009.) (New usage is discouraged.)
⊢ Com2 = {⟨𝑔, ℎ⟩ ∣ ∀𝑎 ∈ ran 𝑔∀𝑏 ∈ ran 𝑔(𝑎ℎ𝑏) = (𝑏ℎ𝑎)}

Syntax	cfld 36859	Extend class notation with the class of all fields.
class Fld

Definition	df-fld 36860	Definition of a field. A field is a commutative division ring. (Contributed by FL, 6-Sep-2009.) (Revised by Jeff Madsen, 10-Jun-2010.) (New usage is discouraged.)
⊢ Fld = (DivRingOps ∩ Com2)

Syntax	ccring 36861	Extend class notation with the class of commutative rings.
class CRingOps

Definition	df-crngo 36862	Define the class of commutative rings. (Contributed by Jeff Madsen, 8-Jun-2010.)
⊢ CRingOps = (RingOps ∩ Com2)

Theorem	iscom2 36863*	A device to add commutativity to various sorts of rings. (Contributed by FL, 6-Sep-2009.) (New usage is discouraged.)
⊢ ((𝐺 ∈ 𝐴 ∧ 𝐻 ∈ 𝐵) → (⟨𝐺, 𝐻⟩ ∈ Com2 ↔ ∀𝑎 ∈ ran 𝐺∀𝑏 ∈ ran 𝐺(𝑎𝐻𝑏) = (𝑏𝐻𝑎)))

Theorem	iscrngo 36864	The predicate "is a commutative ring". (Contributed by Jeff Madsen, 8-Jun-2010.)
⊢ (𝑅 ∈ CRingOps ↔ (𝑅 ∈ RingOps ∧ 𝑅 ∈ Com2))

Theorem	iscrngo2 36865*	The predicate "is a commutative ring". (Contributed by Jeff Madsen, 8-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ (𝑅 ∈ CRingOps ↔ (𝑅 ∈ RingOps ∧ ∀𝑥 ∈ 𝑋 ∀𝑦 ∈ 𝑋 (𝑥𝐻𝑦) = (𝑦𝐻𝑥)))

Theorem	iscringd 36866*	Conditions that determine a commutative ring. (Contributed by Jeff Madsen, 20-Jun-2011.) (Revised by Mario Carneiro, 23-Dec-2013.)
⊢ (𝜑 → 𝐺 ∈ AbelOp) & ⊢ (𝜑 → 𝑋 = ran 𝐺) & ⊢ (𝜑 → 𝐻:(𝑋 × 𝑋)⟶𝑋) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝑋 ∧ 𝑦 ∈ 𝑋 ∧ 𝑧 ∈ 𝑋)) → ((𝑥𝐻𝑦)𝐻𝑧) = (𝑥𝐻(𝑦𝐻𝑧))) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝑋 ∧ 𝑦 ∈ 𝑋 ∧ 𝑧 ∈ 𝑋)) → (𝑥𝐻(𝑦𝐺𝑧)) = ((𝑥𝐻𝑦)𝐺(𝑥𝐻𝑧))) & ⊢ (𝜑 → 𝑈 ∈ 𝑋) & ⊢ ((𝜑 ∧ 𝑦 ∈ 𝑋) → (𝑦𝐻𝑈) = 𝑦) & ⊢ ((𝜑 ∧ (𝑥 ∈ 𝑋 ∧ 𝑦 ∈ 𝑋)) → (𝑥𝐻𝑦) = (𝑦𝐻𝑥)) ⇒ ⊢ (𝜑 → ⟨𝐺, 𝐻⟩ ∈ CRingOps)

Theorem	flddivrng 36867	A field is a division ring. (Contributed by Jeff Madsen, 10-Jun-2010.) (Revised by Mario Carneiro, 15-Dec-2013.) (New usage is discouraged.)
⊢ (𝐾 ∈ Fld → 𝐾 ∈ DivRingOps)

Theorem	crngorngo 36868	A commutative ring is a ring. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ (𝑅 ∈ CRingOps → 𝑅 ∈ RingOps)

Theorem	crngocom 36869	The multiplication operation of a commutative ring is commutative. (Contributed by Jeff Madsen, 8-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ ((𝑅 ∈ CRingOps ∧ 𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) → (𝐴𝐻𝐵) = (𝐵𝐻𝐴))

Theorem	crngm23 36870	Commutative/associative law for commutative rings. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ ((𝑅 ∈ CRingOps ∧ (𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋 ∧ 𝐶 ∈ 𝑋)) → ((𝐴𝐻𝐵)𝐻𝐶) = ((𝐴𝐻𝐶)𝐻𝐵))

Theorem	crngm4 36871	Commutative/associative law for commutative rings. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ ((𝑅 ∈ CRingOps ∧ (𝐴 ∈ 𝑋 ∧ 𝐵 ∈ 𝑋) ∧ (𝐶 ∈ 𝑋 ∧ 𝐷 ∈ 𝑋)) → ((𝐴𝐻𝐵)𝐻(𝐶𝐻𝐷)) = ((𝐴𝐻𝐶)𝐻(𝐵𝐻𝐷)))

Theorem	fldcrngo 36872	A field is a commutative ring. (Contributed by Jeff Madsen, 8-Jun-2010.)
⊢ (𝐾 ∈ Fld → 𝐾 ∈ CRingOps)

Theorem	isfld2 36873	The predicate "is a field". (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ (𝐾 ∈ Fld ↔ (𝐾 ∈ DivRingOps ∧ 𝐾 ∈ CRingOps))

Theorem	crngohomfo 36874	The image of a homomorphism from a commutative ring is commutative. (Contributed by Jeff Madsen, 4-Jan-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝐽 = (1^st ‘𝑆) & ⊢ 𝑌 = ran 𝐽 ⇒ ⊢ (((𝑅 ∈ CRingOps ∧ 𝑆 ∈ RingOps) ∧ (𝐹 ∈ (𝑅 RngHom 𝑆) ∧ 𝐹:𝑋–onto→𝑌)) → 𝑆 ∈ CRingOps)

21.22.20 Ideals

Syntax	cidl 36875	Extend class notation with the class of ideals.
class Idl

Syntax	cpridl 36876	Extend class notation with the class of prime ideals.
class PrIdl

Syntax	cmaxidl 36877	Extend class notation with the class of maximal ideals.
class MaxIdl

Definition	df-idl 36878*	Define the class of (two-sided) ideals of a ring 𝑅. A subset of 𝑅 is an ideal if it contains 0, is closed under addition, and is closed under multiplication on either side by any element of 𝑅. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ Idl = (𝑟 ∈ RingOps ↦ {𝑖 ∈ 𝒫 ran (1^st ‘𝑟) ∣ ((GId‘(1^st ‘𝑟)) ∈ 𝑖 ∧ ∀𝑥 ∈ 𝑖 (∀𝑦 ∈ 𝑖 (𝑥(1^st ‘𝑟)𝑦) ∈ 𝑖 ∧ ∀𝑧 ∈ ran (1^st ‘𝑟)((𝑧(2^nd ‘𝑟)𝑥) ∈ 𝑖 ∧ (𝑥(2^nd ‘𝑟)𝑧) ∈ 𝑖)))})

Definition	df-pridl 36879*	Define the class of prime ideals of a ring 𝑅. A proper ideal 𝐼 of 𝑅 is prime if whenever 𝐴𝐵 ⊆ 𝐼 for ideals 𝐴 and 𝐵, either 𝐴 ⊆ 𝐼 or 𝐵 ⊆ 𝐼. The more familiar definition using elements rather than ideals is equivalent provided 𝑅 is commutative; see ispridl2 36906 and ispridlc 36938. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ PrIdl = (𝑟 ∈ RingOps ↦ {𝑖 ∈ (Idl‘𝑟) ∣ (𝑖 ≠ ran (1^st ‘𝑟) ∧ ∀𝑎 ∈ (Idl‘𝑟)∀𝑏 ∈ (Idl‘𝑟)(∀𝑥 ∈ 𝑎 ∀𝑦 ∈ 𝑏 (𝑥(2^nd ‘𝑟)𝑦) ∈ 𝑖 → (𝑎 ⊆ 𝑖 ∨ 𝑏 ⊆ 𝑖)))})

Definition	df-maxidl 36880*	Define the class of maximal ideals of a ring 𝑅. A proper ideal is called maximal if it is maximal with respect to inclusion among proper ideals. (Contributed by Jeff Madsen, 5-Jan-2011.)
⊢ MaxIdl = (𝑟 ∈ RingOps ↦ {𝑖 ∈ (Idl‘𝑟) ∣ (𝑖 ≠ ran (1^st ‘𝑟) ∧ ∀𝑗 ∈ (Idl‘𝑟)(𝑖 ⊆ 𝑗 → (𝑗 = 𝑖 ∨ 𝑗 = ran (1^st ‘𝑟))))})

Theorem	idlval 36881*	The class of ideals of a ring. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑍 = (GId‘𝐺) ⇒ ⊢ (𝑅 ∈ RingOps → (Idl‘𝑅) = {𝑖 ∈ 𝒫 𝑋 ∣ (𝑍 ∈ 𝑖 ∧ ∀𝑥 ∈ 𝑖 (∀𝑦 ∈ 𝑖 (𝑥𝐺𝑦) ∈ 𝑖 ∧ ∀𝑧 ∈ 𝑋 ((𝑧𝐻𝑥) ∈ 𝑖 ∧ (𝑥𝐻𝑧) ∈ 𝑖)))})

Theorem	isidl 36882*	The predicate "is an ideal of the ring 𝑅". (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑍 = (GId‘𝐺) ⇒ ⊢ (𝑅 ∈ RingOps → (𝐼 ∈ (Idl‘𝑅) ↔ (𝐼 ⊆ 𝑋 ∧ 𝑍 ∈ 𝐼 ∧ ∀𝑥 ∈ 𝐼 (∀𝑦 ∈ 𝐼 (𝑥𝐺𝑦) ∈ 𝐼 ∧ ∀𝑧 ∈ 𝑋 ((𝑧𝐻𝑥) ∈ 𝐼 ∧ (𝑥𝐻𝑧) ∈ 𝐼)))))

Theorem	isidlc 36883*	The predicate "is an ideal of the commutative ring 𝑅". (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑍 = (GId‘𝐺) ⇒ ⊢ (𝑅 ∈ CRingOps → (𝐼 ∈ (Idl‘𝑅) ↔ (𝐼 ⊆ 𝑋 ∧ 𝑍 ∈ 𝐼 ∧ ∀𝑥 ∈ 𝐼 (∀𝑦 ∈ 𝐼 (𝑥𝐺𝑦) ∈ 𝐼 ∧ ∀𝑧 ∈ 𝑋 (𝑧𝐻𝑥) ∈ 𝐼))))

Theorem	idlss 36884	An ideal of 𝑅 is a subset of 𝑅. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅)) → 𝐼 ⊆ 𝑋)

Theorem	idlcl 36885	An element of an ideal is an element of the ring. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅)) ∧ 𝐴 ∈ 𝐼) → 𝐴 ∈ 𝑋)

Theorem	idl0cl 36886	An ideal contains 0. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑍 = (GId‘𝐺) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅)) → 𝑍 ∈ 𝐼)

Theorem	idladdcl 36887	An ideal is closed under addition. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅)) ∧ (𝐴 ∈ 𝐼 ∧ 𝐵 ∈ 𝐼)) → (𝐴𝐺𝐵) ∈ 𝐼)

Theorem	idllmulcl 36888	An ideal is closed under multiplication on the left. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅)) ∧ (𝐴 ∈ 𝐼 ∧ 𝐵 ∈ 𝑋)) → (𝐵𝐻𝐴) ∈ 𝐼)

Theorem	idlrmulcl 36889	An ideal is closed under multiplication on the right. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅)) ∧ (𝐴 ∈ 𝐼 ∧ 𝐵 ∈ 𝑋)) → (𝐴𝐻𝐵) ∈ 𝐼)

Theorem	idlnegcl 36890	An ideal is closed under negation. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑁 = (inv‘𝐺) ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅)) ∧ 𝐴 ∈ 𝐼) → (𝑁‘𝐴) ∈ 𝐼)

Theorem	idlsubcl 36891	An ideal is closed under subtraction. (Contributed by Jeff Madsen, 19-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐷 = ( /_𝑔 ‘𝐺) ⇒ ⊢ (((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅)) ∧ (𝐴 ∈ 𝐼 ∧ 𝐵 ∈ 𝐼)) → (𝐴𝐷𝐵) ∈ 𝐼)

Theorem	rngoidl 36892	A ring 𝑅 is an 𝑅 ideal. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑋 = ran 𝐺 ⇒ ⊢ (𝑅 ∈ RingOps → 𝑋 ∈ (Idl‘𝑅))

Theorem	0idl 36893	The set containing only 0 is an ideal. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝑍 = (GId‘𝐺) ⇒ ⊢ (𝑅 ∈ RingOps → {𝑍} ∈ (Idl‘𝑅))

Theorem	1idl 36894	Two ways of expressing the unit ideal. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅)) → (𝑈 ∈ 𝐼 ↔ 𝐼 = 𝑋))

Theorem	0rngo 36895	In a ring, 0 = 1 iff the ring contains only 0. (Contributed by Jeff Madsen, 6-Jan-2011.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑍 = (GId‘𝐺) & ⊢ 𝑈 = (GId‘𝐻) ⇒ ⊢ (𝑅 ∈ RingOps → (𝑍 = 𝑈 ↔ 𝑋 = {𝑍}))

Theorem	divrngidl 36896	The only ideals in a division ring are the zero ideal and the unit ideal. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ 𝐺 = (1^st ‘𝑅) & ⊢ 𝐻 = (2^nd ‘𝑅) & ⊢ 𝑋 = ran 𝐺 & ⊢ 𝑍 = (GId‘𝐺) ⇒ ⊢ (𝑅 ∈ DivRingOps → (Idl‘𝑅) = {{𝑍}, 𝑋})

Theorem	intidl 36897	The intersection of a nonempty collection of ideals is an ideal. (Contributed by Jeff Madsen, 10-Jun-2010.)
⊢ ((𝑅 ∈ RingOps ∧ 𝐶 ≠ ∅ ∧ 𝐶 ⊆ (Idl‘𝑅)) → ∩ 𝐶 ∈ (Idl‘𝑅))

Theorem	inidl 36898	The intersection of two ideals is an ideal. (Contributed by Jeff Madsen, 16-Jun-2011.)
⊢ ((𝑅 ∈ RingOps ∧ 𝐼 ∈ (Idl‘𝑅) ∧ 𝐽 ∈ (Idl‘𝑅)) → (𝐼 ∩ 𝐽) ∈ (Idl‘𝑅))

Theorem	unichnidl 36899*	The union of a nonempty chain of ideals is an ideal. (Contributed by Jeff Madsen, 5-Jan-2011.)
⊢ ((𝑅 ∈ RingOps ∧ (𝐶 ≠ ∅ ∧ 𝐶 ⊆ (Idl‘𝑅) ∧ ∀𝑖 ∈ 𝐶 ∀𝑗 ∈ 𝐶 (𝑖 ⊆ 𝑗 ∨ 𝑗 ⊆ 𝑖))) → ∪ 𝐶 ∈ (Idl‘𝑅))

Theorem	keridl 36900	The kernel of a ring homomorphism is an ideal. (Contributed by Jeff Madsen, 3-Jan-2011.)
⊢ 𝐺 = (1^st ‘𝑆) & ⊢ 𝑍 = (GId‘𝐺) ⇒ ⊢ ((𝑅 ∈ RingOps ∧ 𝑆 ∈ RingOps ∧ 𝐹 ∈ (𝑅 RngHom 𝑆)) → (^◡𝐹 “ {𝑍}) ∈ (Idl‘𝑅))

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