Documentation

Mathlib.Algebra.Ring.Subring.Basic

Subrings #

Let R be a ring. This file defines the "bundled" subring type Subring R, a type whose terms correspond to subrings of R. This is the preferred way to talk about subrings in mathlib. Unbundled subrings (s : Set R and IsSubring s) are not in this file, and they will ultimately be deprecated.

We prove that subrings are a complete lattice, and that you can map (pushforward) and comap (pull back) them along ring homomorphisms.

We define the closure construction from Set R to Subring R, sending a subset of R to the subring it generates, and prove that it is a Galois insertion.

Main definitions #

Notation used here:

(R : Type u) [Ring R] (S : Type u) [Ring S] (f g : R →+* S) (A : Subring R) (B : Subring S) (s : Set R)

Implementation notes #

A subring is implemented as a subsemiring which is also an additive subgroup. The initial PR was as a submonoid which is also an additive subgroup.

Lattice inclusion (e.g. and ) is used rather than set notation ( and ), although is defined as membership of a subring's underlying set.

Tags #

subring, subrings

class SubringClass (S : Type u_1) (R : outParam (Type u)) [Ring R] [SetLike S R] extends SubsemiringClass , NegMemClass :

SubringClass S R states that S is a type of subsets s ⊆ R that are both a multiplicative submonoid and an additive subgroup.

    Instances
      @[instance 100]
      instance SubringClass.addSubgroupClass (S : Type u_1) (R : Type u) [SetLike S R] [Ring R] [h : SubringClass S R] :
      Equations
      • =
      theorem intCast_mem {R : Type u} {S : Type v} [Ring R] [SetLike S R] [hSR : SubringClass S R] (s : S) (n : ) :
      n s
      @[deprecated intCast_mem]
      theorem coe_int_mem {R : Type u} {S : Type v} [Ring R] [SetLike S R] [hSR : SubringClass S R] (s : S) (n : ) :
      n s

      Alias of intCast_mem.

      @[instance 75]
      instance SubringClass.toHasIntCast {R : Type u} {S : Type v} [Ring R] [SetLike S R] [hSR : SubringClass S R] (s : S) :
      IntCast s
      Equations
      @[instance 75]
      instance SubringClass.toRing {R : Type u} {S : Type v} [Ring R] [SetLike S R] [hSR : SubringClass S R] (s : S) :
      Ring s

      A subring of a ring inherits a ring structure

      Equations
      @[instance 75]
      instance SubringClass.toCommRing {S : Type v} (s : S) {R : Type u_1} [CommRing R] [SetLike S R] [SubringClass S R] :

      A subring of a CommRing is a CommRing.

      Equations
      @[instance 75]
      instance SubringClass.instIsDomainSubtypeMem {S : Type v} (s : S) {R : Type u_1} [Ring R] [IsDomain R] [SetLike S R] [SubringClass S R] :

      A subring of a domain is a domain.

      Equations
      • =
      def SubringClass.subtype {R : Type u} {S : Type v} [Ring R] [SetLike S R] [hSR : SubringClass S R] (s : S) :
      s →+* R

      The natural ring hom from a subring of ring R to R.

      Equations
      • SubringClass.subtype s = { toFun := Subtype.val, map_one' := , map_mul' := , map_zero' := , map_add' := }
      Instances For
        @[simp]
        theorem SubringClass.coeSubtype {R : Type u} {S : Type v} [Ring R] [SetLike S R] [hSR : SubringClass S R] (s : S) :
        (SubringClass.subtype s) = Subtype.val
        @[simp]
        theorem SubringClass.coe_natCast {R : Type u} {S : Type v} [Ring R] [SetLike S R] [hSR : SubringClass S R] (s : S) (n : ) :
        n = n
        @[simp]
        theorem SubringClass.coe_intCast {R : Type u} {S : Type v} [Ring R] [SetLike S R] [hSR : SubringClass S R] (s : S) (n : ) :
        n = n
        structure Subring (R : Type u) [Ring R] extends Subsemiring :

        Subring R is the type of subrings of R. A subring of R is a subset s that is a multiplicative submonoid and an additive subgroup. Note in particular that it shares the same 0 and 1 as R.

        • carrier : Set R
        • mul_mem' : ∀ {a b : R}, a self.carrierb self.carriera * b self.carrier
        • one_mem' : 1 self.carrier
        • add_mem' : ∀ {a b : R}, a self.carrierb self.carriera + b self.carrier
        • zero_mem' : 0 self.carrier
        • neg_mem' : ∀ {x : R}, x self.carrier-x self.carrier

          G is closed under negation

        Instances For
          @[reducible]
          abbrev Subring.toAddSubgroup {R : Type u} [Ring R] (self : Subring R) :

          Reinterpret a Subring as an AddSubgroup.

          Equations
          • self.toAddSubgroup = { carrier := self.carrier, add_mem' := , zero_mem' := , neg_mem' := }
          Instances For
            instance Subring.instSetLike {R : Type u} [Ring R] :
            Equations
            • Subring.instSetLike = { coe := fun (s : Subring R) => s.carrier, coe_injective' := }
            Equations
            • =
            @[simp]
            theorem Subring.mem_toSubsemiring {R : Type u} [Ring R] {s : Subring R} {x : R} :
            x s.toSubsemiring x s
            theorem Subring.mem_carrier {R : Type u} [Ring R] {s : Subring R} {x : R} :
            x s.carrier x s
            @[simp]
            theorem Subring.mem_mk {R : Type u} [Ring R] {S : Subsemiring R} {x : R} (h : ∀ {x : R}, x S.carrier-x S.carrier) :
            x { toSubsemiring := S, neg_mem' := h } x S
            @[simp]
            theorem Subring.coe_set_mk {R : Type u} [Ring R] (S : Subsemiring R) (h : ∀ {x : R}, x S.carrier-x S.carrier) :
            { toSubsemiring := S, neg_mem' := h } = S
            @[simp]
            theorem Subring.mk_le_mk {R : Type u} [Ring R] {S : Subsemiring R} {S' : Subsemiring R} (h₁ : ∀ {x : R}, x S.carrier-x S.carrier) (h₂ : ∀ {x : R}, x S'.carrier-x S'.carrier) :
            { toSubsemiring := S, neg_mem' := h₁ } { toSubsemiring := S', neg_mem' := h₂ } S S'
            theorem Subring.ext_iff {R : Type u} [Ring R] {S : Subring R} {T : Subring R} :
            S = T ∀ (x : R), x S x T
            theorem Subring.ext {R : Type u} [Ring R] {S : Subring R} {T : Subring R} (h : ∀ (x : R), x S x T) :
            S = T

            Two subrings are equal if they have the same elements.

            def Subring.copy {R : Type u} [Ring R] (S : Subring R) (s : Set R) (hs : s = S) :

            Copy of a subring with a new carrier equal to the old one. Useful to fix definitional equalities.

            Equations
            • S.copy s hs = { carrier := s, mul_mem' := , one_mem' := , add_mem' := , zero_mem' := , neg_mem' := }
            Instances For
              @[simp]
              theorem Subring.coe_copy {R : Type u} [Ring R] (S : Subring R) (s : Set R) (hs : s = S) :
              (S.copy s hs) = s
              theorem Subring.copy_eq {R : Type u} [Ring R] (S : Subring R) (s : Set R) (hs : s = S) :
              S.copy s hs = S
              theorem Subring.toSubsemiring_injective {R : Type u} [Ring R] :
              Function.Injective Subring.toSubsemiring
              theorem Subring.toSubsemiring_strictMono {R : Type u} [Ring R] :
              StrictMono Subring.toSubsemiring
              theorem Subring.toSubsemiring_mono {R : Type u} [Ring R] :
              Monotone Subring.toSubsemiring
              theorem Subring.toAddSubgroup_injective {R : Type u} [Ring R] :
              Function.Injective Subring.toAddSubgroup
              theorem Subring.toAddSubgroup_strictMono {R : Type u} [Ring R] :
              StrictMono Subring.toAddSubgroup
              theorem Subring.toAddSubgroup_mono {R : Type u} [Ring R] :
              Monotone Subring.toAddSubgroup
              theorem Subring.toSubmonoid_injective {R : Type u} [Ring R] :
              Function.Injective fun (s : Subring R) => s.toSubmonoid
              theorem Subring.toSubmonoid_strictMono {R : Type u} [Ring R] :
              StrictMono fun (s : Subring R) => s.toSubmonoid
              theorem Subring.toSubmonoid_mono {R : Type u} [Ring R] :
              Monotone fun (s : Subring R) => s.toSubmonoid
              def Subring.mk' {R : Type u} [Ring R] (s : Set R) (sm : Submonoid R) (sa : AddSubgroup R) (hm : sm = s) (ha : sa = s) :

              Construct a Subring R from a set s, a submonoid sm, and an additive subgroup sa such that x ∈ s ↔ x ∈ sm ↔ x ∈ sa.

              Equations
              • Subring.mk' s sm sa hm ha = { toSubmonoid := sm.copy s , add_mem' := , zero_mem' := , neg_mem' := }
              Instances For
                @[simp]
                theorem Subring.coe_mk' {R : Type u} [Ring R] {s : Set R} {sm : Submonoid R} (hm : sm = s) {sa : AddSubgroup R} (ha : sa = s) :
                (Subring.mk' s sm sa hm ha) = s
                @[simp]
                theorem Subring.mem_mk' {R : Type u} [Ring R] {s : Set R} {sm : Submonoid R} (hm : sm = s) {sa : AddSubgroup R} (ha : sa = s) {x : R} :
                x Subring.mk' s sm sa hm ha x s
                @[simp]
                theorem Subring.mk'_toSubmonoid {R : Type u} [Ring R] {s : Set R} {sm : Submonoid R} (hm : sm = s) {sa : AddSubgroup R} (ha : sa = s) :
                (Subring.mk' s sm sa hm ha).toSubmonoid = sm
                @[simp]
                theorem Subring.mk'_toAddSubgroup {R : Type u} [Ring R] {s : Set R} {sm : Submonoid R} (hm : sm = s) {sa : AddSubgroup R} (ha : sa = s) :
                (Subring.mk' s sm sa hm ha).toAddSubgroup = sa
                def Subsemiring.toSubring {R : Type u} [Ring R] (s : Subsemiring R) (hneg : -1 s) :

                A Subsemiring containing -1 is a Subring.

                Equations
                • s.toSubring hneg = { toSubsemiring := s, neg_mem' := }
                Instances For
                  theorem Subring.one_mem {R : Type u} [Ring R] (s : Subring R) :
                  1 s

                  A subring contains the ring's 1.

                  theorem Subring.zero_mem {R : Type u} [Ring R] (s : Subring R) :
                  0 s

                  A subring contains the ring's 0.

                  theorem Subring.mul_mem {R : Type u} [Ring R] (s : Subring R) {x : R} {y : R} :
                  x sy sx * y s

                  A subring is closed under multiplication.

                  theorem Subring.add_mem {R : Type u} [Ring R] (s : Subring R) {x : R} {y : R} :
                  x sy sx + y s

                  A subring is closed under addition.

                  theorem Subring.neg_mem {R : Type u} [Ring R] (s : Subring R) {x : R} :
                  x s-x s

                  A subring is closed under negation.

                  theorem Subring.sub_mem {R : Type u} [Ring R] (s : Subring R) {x : R} {y : R} (hx : x s) (hy : y s) :
                  x - y s

                  A subring is closed under subtraction

                  theorem Subring.list_prod_mem {R : Type u} [Ring R] (s : Subring R) {l : List R} :
                  (∀ xl, x s)l.prod s

                  Product of a list of elements in a subring is in the subring.

                  theorem Subring.list_sum_mem {R : Type u} [Ring R] (s : Subring R) {l : List R} :
                  (∀ xl, x s)l.sum s

                  Sum of a list of elements in a subring is in the subring.

                  theorem Subring.multiset_prod_mem {R : Type u_1} [CommRing R] (s : Subring R) (m : Multiset R) :
                  (∀ am, a s)m.prod s

                  Product of a multiset of elements in a subring of a CommRing is in the subring.

                  theorem Subring.multiset_sum_mem {R : Type u_1} [Ring R] (s : Subring R) (m : Multiset R) :
                  (∀ am, a s)m.sum s

                  Sum of a multiset of elements in a Subring of a Ring is in the Subring.

                  theorem Subring.prod_mem {R : Type u_1} [CommRing R] (s : Subring R) {ι : Type u_2} {t : Finset ι} {f : ιR} (h : ct, f c s) :
                  it, f i s

                  Product of elements of a subring of a CommRing indexed by a Finset is in the subring.

                  theorem Subring.sum_mem {R : Type u_1} [Ring R] (s : Subring R) {ι : Type u_2} {t : Finset ι} {f : ιR} (h : ct, f c s) :
                  it, f i s

                  Sum of elements in a Subring of a Ring indexed by a Finset is in the Subring.

                  instance Subring.toRing {R : Type u} [Ring R] (s : Subring R) :
                  Ring s

                  A subring of a ring inherits a ring structure

                  Equations
                  theorem Subring.zsmul_mem {R : Type u} [Ring R] (s : Subring R) {x : R} (hx : x s) (n : ) :
                  n x s
                  theorem Subring.pow_mem {R : Type u} [Ring R] (s : Subring R) {x : R} (hx : x s) (n : ) :
                  x ^ n s
                  @[simp]
                  theorem Subring.coe_add {R : Type u} [Ring R] (s : Subring R) (x : s) (y : s) :
                  (x + y) = x + y
                  @[simp]
                  theorem Subring.coe_neg {R : Type u} [Ring R] (s : Subring R) (x : s) :
                  (-x) = -x
                  @[simp]
                  theorem Subring.coe_mul {R : Type u} [Ring R] (s : Subring R) (x : s) (y : s) :
                  (x * y) = x * y
                  @[simp]
                  theorem Subring.coe_zero {R : Type u} [Ring R] (s : Subring R) :
                  0 = 0
                  @[simp]
                  theorem Subring.coe_one {R : Type u} [Ring R] (s : Subring R) :
                  1 = 1
                  @[simp]
                  theorem Subring.coe_pow {R : Type u} [Ring R] (s : Subring R) (x : s) (n : ) :
                  (x ^ n) = x ^ n
                  theorem Subring.coe_eq_zero_iff {R : Type u} [Ring R] (s : Subring R) {x : s} :
                  x = 0 x = 0
                  instance Subring.toCommRing {R : Type u_1} [CommRing R] (s : Subring R) :

                  A subring of a CommRing is a CommRing.

                  Equations
                  instance Subring.instNontrivialSubtypeMem {R : Type u_1} [Ring R] [Nontrivial R] (s : Subring R) :

                  A subring of a non-trivial ring is non-trivial.

                  Equations
                  • =

                  A subring of a ring with no zero divisors has no zero divisors.

                  Equations
                  • =
                  instance Subring.instIsDomainSubtypeMem {R : Type u_1} [Ring R] [IsDomain R] (s : Subring R) :

                  A subring of a domain is a domain.

                  Equations
                  • =
                  def Subring.subtype {R : Type u} [Ring R] (s : Subring R) :
                  s →+* R

                  The natural ring hom from a subring of ring R to R.

                  Equations
                  • s.subtype = { toFun := Subtype.val, map_one' := , map_mul' := , map_zero' := , map_add' := }
                  Instances For
                    @[simp]
                    theorem Subring.coeSubtype {R : Type u} [Ring R] (s : Subring R) :
                    s.subtype = Subtype.val
                    theorem Subring.coe_natCast {R : Type u} [Ring R] (s : Subring R) (n : ) :
                    n = n
                    theorem Subring.coe_intCast {R : Type u} [Ring R] (s : Subring R) (n : ) :
                    n = n

                    Partial order #

                    @[simp]
                    theorem Subring.coe_toSubsemiring {R : Type u} [Ring R] (s : Subring R) :
                    s.toSubsemiring = s
                    @[simp]
                    theorem Subring.mem_toSubmonoid {R : Type u} [Ring R] {s : Subring R} {x : R} :
                    x s.toSubmonoid x s
                    @[simp]
                    theorem Subring.coe_toSubmonoid {R : Type u} [Ring R] (s : Subring R) :
                    s.toSubmonoid = s
                    @[simp]
                    theorem Subring.mem_toAddSubgroup {R : Type u} [Ring R] {s : Subring R} {x : R} :
                    x s.toAddSubgroup x s
                    @[simp]
                    theorem Subring.coe_toAddSubgroup {R : Type u} [Ring R] (s : Subring R) :
                    s.toAddSubgroup = s

                    top #

                    instance Subring.instTop {R : Type u} [Ring R] :

                    The subring R of the ring R.

                    Equations
                    • Subring.instTop = { top := let __src := ; let __src_1 := ; { toSubmonoid := __src, add_mem' := , zero_mem' := , neg_mem' := } }
                    @[simp]
                    theorem Subring.mem_top {R : Type u} [Ring R] (x : R) :
                    @[simp]
                    theorem Subring.coe_top {R : Type u} [Ring R] :
                    = Set.univ
                    @[simp]
                    theorem Subring.topEquiv_apply {R : Type u} [Ring R] (r : ) :
                    Subring.topEquiv r = r
                    @[simp]
                    theorem Subring.topEquiv_symm_apply_coe {R : Type u} [Ring R] (r : R) :
                    (Subring.topEquiv.symm r) = r
                    def Subring.topEquiv {R : Type u} [Ring R] :
                    ≃+* R

                    The ring equiv between the top element of Subring R and R.

                    Equations
                    • Subring.topEquiv = Subsemiring.topEquiv
                    Instances For
                      Equations

                      comap #

                      def Subring.comap {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (s : Subring S) :

                      The preimage of a subring along a ring homomorphism is a subring.

                      Equations
                      • Subring.comap f s = { carrier := f ⁻¹' s.carrier, mul_mem' := , one_mem' := , add_mem' := , zero_mem' := , neg_mem' := }
                      Instances For
                        @[simp]
                        theorem Subring.coe_comap {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring S) (f : R →+* S) :
                        (Subring.comap f s) = f ⁻¹' s
                        @[simp]
                        theorem Subring.mem_comap {R : Type u} {S : Type v} [Ring R] [Ring S] {s : Subring S} {f : R →+* S} {x : R} :
                        x Subring.comap f s f x s
                        theorem Subring.comap_comap {R : Type u} {S : Type v} {T : Type w} [Ring R] [Ring S] [Ring T] (s : Subring T) (g : S →+* T) (f : R →+* S) :

                        map #

                        def Subring.map {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (s : Subring R) :

                        The image of a subring along a ring homomorphism is a subring.

                        Equations
                        • Subring.map f s = { carrier := f '' s.carrier, mul_mem' := , one_mem' := , add_mem' := , zero_mem' := , neg_mem' := }
                        Instances For
                          @[simp]
                          theorem Subring.coe_map {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (s : Subring R) :
                          (Subring.map f s) = f '' s
                          @[simp]
                          theorem Subring.mem_map {R : Type u} {S : Type v} [Ring R] [Ring S] {f : R →+* S} {s : Subring R} {y : S} :
                          y Subring.map f s xs, f x = y
                          @[simp]
                          theorem Subring.map_id {R : Type u} [Ring R] (s : Subring R) :
                          theorem Subring.map_map {R : Type u} {S : Type v} {T : Type w} [Ring R] [Ring S] [Ring T] (s : Subring R) (g : S →+* T) (f : R →+* S) :
                          Subring.map g (Subring.map f s) = Subring.map (g.comp f) s
                          theorem Subring.map_le_iff_le_comap {R : Type u} {S : Type v} [Ring R] [Ring S] {f : R →+* S} {s : Subring R} {t : Subring S} :
                          theorem Subring.gc_map_comap {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) :
                          noncomputable def Subring.equivMapOfInjective {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) (f : R →+* S) (hf : Function.Injective f) :
                          s ≃+* (Subring.map f s)

                          A subring is isomorphic to its image under an injective function

                          Equations
                          • s.equivMapOfInjective f hf = { toEquiv := Equiv.Set.image (⇑f) (↑s) hf, map_mul' := , map_add' := }
                          Instances For
                            @[simp]
                            theorem Subring.coe_equivMapOfInjective_apply {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) (f : R →+* S) (hf : Function.Injective f) (x : s) :
                            ((s.equivMapOfInjective f hf) x) = f x

                            range #

                            def RingHom.range {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) :

                            The range of a ring homomorphism, as a subring of the target. See Note [range copy pattern].

                            Equations
                            Instances For
                              @[simp]
                              theorem RingHom.coe_range {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) :
                              f.range = Set.range f
                              @[simp]
                              theorem RingHom.mem_range {R : Type u} {S : Type v} [Ring R] [Ring S] {f : R →+* S} {y : S} :
                              y f.range ∃ (x : R), f x = y
                              theorem RingHom.range_eq_map {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) :
                              f.range = Subring.map f
                              theorem RingHom.mem_range_self {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (x : R) :
                              f x f.range
                              theorem RingHom.map_range {R : Type u} {S : Type v} {T : Type w} [Ring R] [Ring S] [Ring T] (g : S →+* T) (f : R →+* S) :
                              Subring.map g f.range = (g.comp f).range
                              instance RingHom.fintypeRange {R : Type u} {S : Type v} [Ring R] [Ring S] [Fintype R] [DecidableEq S] (f : R →+* S) :
                              Fintype f.range

                              The range of a ring homomorphism is a fintype, if the domain is a fintype. Note: this instance can form a diamond with Subtype.fintype in the presence of Fintype S.

                              Equations

                              bot #

                              instance Subring.instBot {R : Type u} [Ring R] :
                              Equations
                              instance Subring.instInhabited {R : Type u} [Ring R] :
                              Equations
                              • Subring.instInhabited = { default := }
                              theorem Subring.coe_bot {R : Type u} [Ring R] :
                              = Set.range Int.cast
                              theorem Subring.mem_bot {R : Type u} [Ring R] {x : R} :
                              x ∃ (n : ), n = x

                              inf #

                              instance Subring.instInf {R : Type u} [Ring R] :

                              The inf of two subrings is their intersection.

                              Equations
                              • One or more equations did not get rendered due to their size.
                              @[simp]
                              theorem Subring.coe_inf {R : Type u} [Ring R] (p : Subring R) (p' : Subring R) :
                              (p p') = p p'
                              @[simp]
                              theorem Subring.mem_inf {R : Type u} [Ring R] {p : Subring R} {p' : Subring R} {x : R} :
                              x p p' x p x p'
                              instance Subring.instInfSet {R : Type u} [Ring R] :
                              Equations
                              • Subring.instInfSet = { sInf := fun (s : Set (Subring R)) => Subring.mk' (⋂ ts, t) (⨅ ts, t.toSubmonoid) (⨅ ts, t.toAddSubgroup) }
                              @[simp]
                              theorem Subring.coe_sInf {R : Type u} [Ring R] (S : Set (Subring R)) :
                              (sInf S) = sS, s
                              theorem Subring.mem_sInf {R : Type u} [Ring R] {S : Set (Subring R)} {x : R} :
                              x sInf S pS, x p
                              @[simp]
                              theorem Subring.coe_iInf {R : Type u} [Ring R] {ι : Sort u_1} {S : ιSubring R} :
                              (⨅ (i : ι), S i) = ⋂ (i : ι), (S i)
                              theorem Subring.mem_iInf {R : Type u} [Ring R] {ι : Sort u_1} {S : ιSubring R} {x : R} :
                              x ⨅ (i : ι), S i ∀ (i : ι), x S i
                              @[simp]
                              theorem Subring.sInf_toSubmonoid {R : Type u} [Ring R] (s : Set (Subring R)) :
                              (sInf s).toSubmonoid = ts, t.toSubmonoid
                              @[simp]
                              theorem Subring.sInf_toAddSubgroup {R : Type u} [Ring R] (s : Set (Subring R)) :
                              (sInf s).toAddSubgroup = ts, t.toAddSubgroup

                              Subrings of a ring form a complete lattice.

                              Equations
                              theorem Subring.eq_top_iff' {R : Type u} [Ring R] (A : Subring R) :
                              A = ∀ (x : R), x A

                              Center of a ring #

                              def Subring.center (R : Type u) [Ring R] :

                              The center of a ring R is the set of elements that commute with everything in R

                              Equations
                              • Subring.center R = { carrier := Set.center R, mul_mem' := , one_mem' := , add_mem' := , zero_mem' := , neg_mem' := }
                              Instances For
                                @[simp]
                                theorem Subring.center_toSubsemiring (R : Type u) [Ring R] :
                                (Subring.center R).toSubsemiring = Subsemiring.center R
                                theorem Subring.mem_center_iff {R : Type u} [Ring R] {z : R} :
                                z Subring.center R ∀ (g : R), g * z = z * g
                                instance Subring.decidableMemCenter {R : Type u} [Ring R] [DecidableEq R] [Fintype R] :
                                DecidablePred fun (x : R) => x Subring.center R
                                Equations
                                @[simp]

                                The center is commutative.

                                Equations
                                Equations
                                @[simp]
                                theorem Subring.center.coe_inv {K : Type u} [DivisionRing K] (a : (Subring.center K)) :
                                a⁻¹ = (↑a)⁻¹
                                @[simp]
                                theorem Subring.center.coe_div {K : Type u} [DivisionRing K] (a : (Subring.center K)) (b : (Subring.center K)) :
                                (a / b) = a / b
                                def Subring.centralizer {R : Type u} [Ring R] (s : Set R) :

                                The centralizer of a set inside a ring as a Subring.

                                Equations
                                Instances For
                                  @[simp]
                                  theorem Subring.coe_centralizer {R : Type u} [Ring R] (s : Set R) :
                                  (Subring.centralizer s) = s.centralizer
                                  theorem Subring.mem_centralizer_iff {R : Type u} [Ring R] {s : Set R} {z : R} :
                                  z Subring.centralizer s gs, g * z = z * g
                                  theorem Subring.centralizer_le {R : Type u} [Ring R] (s : Set R) (t : Set R) (h : s t) :

                                  subring closure of a subset #

                                  def Subring.closure {R : Type u} [Ring R] (s : Set R) :

                                  The Subring generated by a set.

                                  Equations
                                  Instances For
                                    theorem Subring.mem_closure {R : Type u} [Ring R] {x : R} {s : Set R} :
                                    x Subring.closure s ∀ (S : Subring R), s Sx S
                                    @[simp]
                                    theorem Subring.subset_closure {R : Type u} [Ring R] {s : Set R} :

                                    The subring generated by a set includes the set.

                                    theorem Subring.not_mem_of_not_mem_closure {R : Type u} [Ring R] {s : Set R} {P : R} (hP : PSubring.closure s) :
                                    Ps
                                    @[simp]
                                    theorem Subring.closure_le {R : Type u} [Ring R] {s : Set R} {t : Subring R} :

                                    A subring t includes closure s if and only if it includes s.

                                    theorem Subring.closure_mono {R : Type u} [Ring R] ⦃s : Set R ⦃t : Set R (h : s t) :

                                    Subring closure of a set is monotone in its argument: if s ⊆ t, then closure s ≤ closure t.

                                    theorem Subring.closure_eq_of_le {R : Type u} [Ring R] {s : Set R} {t : Subring R} (h₁ : s t) (h₂ : t Subring.closure s) :
                                    theorem Subring.closure_induction {R : Type u} [Ring R] {s : Set R} {p : RProp} {x : R} (h : x Subring.closure s) (Hs : xs, p x) (zero : p 0) (one : p 1) (add : ∀ (x y : R), p xp yp (x + y)) (neg : ∀ (x : R), p xp (-x)) (mul : ∀ (x y : R), p xp yp (x * y)) :
                                    p x

                                    An induction principle for closure membership. If p holds for 0, 1, and all elements of s, and is preserved under addition, negation, and multiplication, then p holds for all elements of the closure of s.

                                    theorem Subring.closure_induction' {R : Type u} [Ring R] {s : Set R} {p : (x : R) → x Subring.closure sProp} (mem : ∀ (x : R) (h : x s), p x ) (zero : p 0 ) (one : p 1 ) (add : ∀ (x : R) (hx : x Subring.closure s) (y : R) (hy : y Subring.closure s), p x hxp y hyp (x + y) ) (neg : ∀ (x : R) (hx : x Subring.closure s), p x hxp (-x) ) (mul : ∀ (x : R) (hx : x Subring.closure s) (y : R) (hy : y Subring.closure s), p x hxp y hyp (x * y) ) {a : R} (ha : a Subring.closure s) :
                                    p a ha
                                    theorem Subring.closure_induction₂ {R : Type u} [Ring R] {s : Set R} {p : RRProp} {a : R} {b : R} (ha : a Subring.closure s) (hb : b Subring.closure s) (Hs : xs, ys, p x y) (H0_left : ∀ (x : R), p 0 x) (H0_right : ∀ (x : R), p x 0) (H1_left : ∀ (x : R), p 1 x) (H1_right : ∀ (x : R), p x 1) (Hneg_left : ∀ (x y : R), p x yp (-x) y) (Hneg_right : ∀ (x y : R), p x yp x (-y)) (Hadd_left : ∀ (x₁ x₂ y : R), p x₁ yp x₂ yp (x₁ + x₂) y) (Hadd_right : ∀ (x y₁ y₂ : R), p x y₁p x y₂p x (y₁ + y₂)) (Hmul_left : ∀ (x₁ x₂ y : R), p x₁ yp x₂ yp (x₁ * x₂) y) (Hmul_right : ∀ (x y₁ y₂ : R), p x y₁p x y₂p x (y₁ * y₂)) :
                                    p a b

                                    An induction principle for closure membership, for predicates with two arguments.

                                    def Subring.closureCommRingOfComm {R : Type u} [Ring R] {s : Set R} (hcomm : as, bs, a * b = b * a) :

                                    If all elements of s : Set A commute pairwise, then closure s is a commutative ring.

                                    Equations
                                    Instances For
                                      theorem Subring.exists_list_of_mem_closure {R : Type u} [Ring R] {s : Set R} {x : R} (h : x Subring.closure s) :
                                      ∃ (L : List (List R)), (∀ tL, yt, y s y = -1) (List.map List.prod L).sum = x
                                      def Subring.gi (R : Type u) [Ring R] :
                                      GaloisInsertion Subring.closure SetLike.coe

                                      closure forms a Galois insertion with the coercion to set.

                                      Equations
                                      Instances For
                                        theorem Subring.closure_eq {R : Type u} [Ring R] (s : Subring R) :

                                        Closure of a subring S equals S.

                                        @[simp]
                                        theorem Subring.closure_univ {R : Type u} [Ring R] :
                                        theorem Subring.closure_iUnion {R : Type u} [Ring R] {ι : Sort u_1} (s : ιSet R) :
                                        Subring.closure (⋃ (i : ι), s i) = ⨆ (i : ι), Subring.closure (s i)
                                        theorem Subring.closure_sUnion {R : Type u} [Ring R] (s : Set (Set R)) :
                                        theorem Subring.map_sup {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) (t : Subring R) (f : R →+* S) :
                                        theorem Subring.map_iSup {R : Type u} {S : Type v} [Ring R] [Ring S] {ι : Sort u_1} (f : R →+* S) (s : ιSubring R) :
                                        Subring.map f (iSup s) = ⨆ (i : ι), Subring.map f (s i)
                                        theorem Subring.map_inf {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) (t : Subring R) (f : R →+* S) (hf : Function.Injective f) :
                                        theorem Subring.map_iInf {R : Type u} {S : Type v} [Ring R] [Ring S] {ι : Sort u_1} [Nonempty ι] (f : R →+* S) (hf : Function.Injective f) (s : ιSubring R) :
                                        Subring.map f (iInf s) = ⨅ (i : ι), Subring.map f (s i)
                                        theorem Subring.comap_inf {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring S) (t : Subring S) (f : R →+* S) :
                                        theorem Subring.comap_iInf {R : Type u} {S : Type v} [Ring R] [Ring S] {ι : Sort u_1} (f : R →+* S) (s : ιSubring S) :
                                        Subring.comap f (iInf s) = ⨅ (i : ι), Subring.comap f (s i)
                                        @[simp]
                                        theorem Subring.map_bot {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) :
                                        @[simp]
                                        theorem Subring.comap_top {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) :
                                        def Subring.prod {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) (t : Subring S) :
                                        Subring (R × S)

                                        Given Subrings s, t of rings R, S respectively, s.prod t is s ×̂ t as a subring of R × S.

                                        Equations
                                        • s.prod t = { carrier := s ×ˢ t, mul_mem' := , one_mem' := , add_mem' := , zero_mem' := , neg_mem' := }
                                        Instances For
                                          theorem Subring.coe_prod {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) (t : Subring S) :
                                          (s.prod t) = s ×ˢ t
                                          theorem Subring.mem_prod {R : Type u} {S : Type v} [Ring R] [Ring S] {s : Subring R} {t : Subring S} {p : R × S} :
                                          p s.prod t p.1 s p.2 t
                                          theorem Subring.prod_mono {R : Type u} {S : Type v} [Ring R] [Ring S] ⦃s₁ : Subring R ⦃s₂ : Subring R (hs : s₁ s₂) ⦃t₁ : Subring S ⦃t₂ : Subring S (ht : t₁ t₂) :
                                          s₁.prod t₁ s₂.prod t₂
                                          theorem Subring.prod_mono_right {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) :
                                          Monotone fun (t : Subring S) => s.prod t
                                          theorem Subring.prod_mono_left {R : Type u} {S : Type v} [Ring R] [Ring S] (t : Subring S) :
                                          Monotone fun (s : Subring R) => s.prod t
                                          theorem Subring.prod_top {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) :
                                          theorem Subring.top_prod {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring S) :
                                          @[simp]
                                          theorem Subring.top_prod_top {R : Type u} {S : Type v} [Ring R] [Ring S] :
                                          .prod =
                                          def Subring.prodEquiv {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) (t : Subring S) :
                                          (s.prod t) ≃+* s × t

                                          Product of subrings is isomorphic to their product as rings.

                                          Equations
                                          • s.prodEquiv t = { toEquiv := Equiv.Set.prod s t, map_mul' := , map_add' := }
                                          Instances For
                                            theorem Subring.mem_iSup_of_directed {R : Type u} [Ring R] {ι : Sort u_1} [hι : Nonempty ι] {S : ιSubring R} (hS : Directed (fun (x1 x2 : Subring R) => x1 x2) S) {x : R} :
                                            x ⨆ (i : ι), S i ∃ (i : ι), x S i

                                            The underlying set of a non-empty directed sSup of subrings is just a union of the subrings. Note that this fails without the directedness assumption (the union of two subrings is typically not a subring)

                                            theorem Subring.coe_iSup_of_directed {R : Type u} [Ring R] {ι : Sort u_1} [hι : Nonempty ι] {S : ιSubring R} (hS : Directed (fun (x1 x2 : Subring R) => x1 x2) S) :
                                            (⨆ (i : ι), S i) = ⋃ (i : ι), (S i)
                                            theorem Subring.mem_sSup_of_directedOn {R : Type u} [Ring R] {S : Set (Subring R)} (Sne : S.Nonempty) (hS : DirectedOn (fun (x1 x2 : Subring R) => x1 x2) S) {x : R} :
                                            x sSup S sS, x s
                                            theorem Subring.coe_sSup_of_directedOn {R : Type u} [Ring R] {S : Set (Subring R)} (Sne : S.Nonempty) (hS : DirectedOn (fun (x1 x2 : Subring R) => x1 x2) S) :
                                            (sSup S) = sS, s
                                            theorem Subring.mem_map_equiv {R : Type u} {S : Type v} [Ring R] [Ring S] {f : R ≃+* S} {K : Subring R} {x : S} :
                                            x Subring.map (↑f) K f.symm x K
                                            theorem Subring.map_equiv_eq_comap_symm {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R ≃+* S) (K : Subring R) :
                                            Subring.map (↑f) K = Subring.comap (↑f.symm) K
                                            theorem Subring.comap_equiv_eq_map_symm {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R ≃+* S) (K : Subring S) :
                                            Subring.comap (↑f) K = Subring.map (↑f.symm) K
                                            def RingHom.rangeRestrict {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) :
                                            R →+* f.range

                                            Restriction of a ring homomorphism to its range interpreted as a subsemiring.

                                            This is the bundled version of Set.rangeFactorization.

                                            Equations
                                            • f.rangeRestrict = f.codRestrict f.range
                                            Instances For
                                              @[simp]
                                              theorem RingHom.coe_rangeRestrict {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (x : R) :
                                              (f.rangeRestrict x) = f x
                                              theorem RingHom.rangeRestrict_surjective {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) :
                                              Function.Surjective f.rangeRestrict
                                              theorem RingHom.range_top_iff_surjective {R : Type u} {S : Type v} [Ring R] [Ring S] {f : R →+* S} :
                                              @[simp]
                                              theorem RingHom.range_top_of_surjective {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (hf : Function.Surjective f) :
                                              f.range =

                                              The range of a surjective ring homomorphism is the whole of the codomain.

                                              def RingHom.eqLocus {R : Type u} [Ring R] {S : Type v} [Semiring S] (f : R →+* S) (g : R →+* S) :

                                              The subring of elements x : R such that f x = g x, i.e., the equalizer of f and g as a subring of R

                                              Equations
                                              • f.eqLocus g = { carrier := {x : R | f x = g x}, mul_mem' := , one_mem' := , add_mem' := , zero_mem' := , neg_mem' := }
                                              Instances For
                                                @[simp]
                                                theorem RingHom.eqLocus_same {R : Type u} [Ring R] {S : Type v} [Semiring S] (f : R →+* S) :
                                                f.eqLocus f =
                                                theorem RingHom.eqOn_set_closure {R : Type u} [Ring R] {S : Type v} [Semiring S] {f : R →+* S} {g : R →+* S} {s : Set R} (h : Set.EqOn (⇑f) (⇑g) s) :
                                                Set.EqOn f g (Subring.closure s)

                                                If two ring homomorphisms are equal on a set, then they are equal on its subring closure.

                                                theorem RingHom.eq_of_eqOn_set_top {R : Type u} [Ring R] {S : Type v} [Semiring S] {f : R →+* S} {g : R →+* S} (h : Set.EqOn f g ) :
                                                f = g
                                                theorem RingHom.eq_of_eqOn_set_dense {R : Type u} [Ring R] {S : Type v} [Semiring S] {s : Set R} (hs : Subring.closure s = ) {f : R →+* S} {g : R →+* S} (h : Set.EqOn (⇑f) (⇑g) s) :
                                                f = g
                                                theorem RingHom.closure_preimage_le {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (s : Set S) :
                                                theorem RingHom.map_closure {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (s : Set R) :

                                                The image under a ring homomorphism of the subring generated by a set equals the subring generated by the image of the set.

                                                def Subring.inclusion {R : Type u} [Ring R] {S : Subring R} {T : Subring R} (h : S T) :
                                                S →+* T

                                                The ring homomorphism associated to an inclusion of subrings.

                                                Equations
                                                Instances For
                                                  @[simp]
                                                  theorem Subring.range_subtype {R : Type u} [Ring R] (s : Subring R) :
                                                  s.subtype.range = s
                                                  theorem Subring.range_fst {R : Type u} {S : Type v} [Ring R] [Ring S] :
                                                  (RingHom.fst R S).rangeS =
                                                  theorem Subring.range_snd {R : Type u} {S : Type v} [Ring R] [Ring S] :
                                                  (RingHom.snd R S).rangeS =
                                                  @[simp]
                                                  theorem Subring.prod_bot_sup_bot_prod {R : Type u} {S : Type v} [Ring R] [Ring S] (s : Subring R) (t : Subring S) :
                                                  s.prod .prod t = s.prod t
                                                  def RingEquiv.subringCongr {R : Type u} [Ring R] {s : Subring R} {t : Subring R} (h : s = t) :
                                                  s ≃+* t

                                                  Makes the identity isomorphism from a proof two subrings of a multiplicative monoid are equal.

                                                  Equations
                                                  Instances For
                                                    def RingEquiv.ofLeftInverse {R : Type u} {S : Type v} [Ring R] [Ring S] {g : SR} {f : R →+* S} (h : Function.LeftInverse g f) :
                                                    R ≃+* f.range

                                                    Restrict a ring homomorphism with a left inverse to a ring isomorphism to its RingHom.range.

                                                    Equations
                                                    • RingEquiv.ofLeftInverse h = { toFun := fun (x : R) => f.rangeRestrict x, invFun := fun (x : f.range) => (g f.range.subtype) x, left_inv := h, right_inv := , map_mul' := , map_add' := }
                                                    Instances For
                                                      @[simp]
                                                      theorem RingEquiv.ofLeftInverse_apply {R : Type u} {S : Type v} [Ring R] [Ring S] {g : SR} {f : R →+* S} (h : Function.LeftInverse g f) (x : R) :
                                                      ((RingEquiv.ofLeftInverse h) x) = f x
                                                      @[simp]
                                                      theorem RingEquiv.ofLeftInverse_symm_apply {R : Type u} {S : Type v} [Ring R] [Ring S] {g : SR} {f : R →+* S} (h : Function.LeftInverse g f) (x : f.range) :
                                                      (RingEquiv.ofLeftInverse h).symm x = g x
                                                      @[simp]
                                                      theorem RingEquiv.subringMap_apply_coe {R : Type u} {S : Type v} [Ring R] [Ring S] {s : Subring R} (e : R ≃+* S) (x : s.toAddSubmonoid) :
                                                      (e.subringMap x) = e x
                                                      @[simp]
                                                      theorem RingEquiv.subringMap_symm_apply_coe {R : Type u} {S : Type v} [Ring R] [Ring S] {s : Subring R} (e : R ≃+* S) (y : (e.toAddEquiv '' s.toAddSubmonoid)) :
                                                      (e.subringMap.symm y) = (↑e).symm y
                                                      def RingEquiv.subringMap {R : Type u} {S : Type v} [Ring R] [Ring S] {s : Subring R} (e : R ≃+* S) :
                                                      s ≃+* (Subring.map e.toRingHom s)

                                                      Given an equivalence e : R ≃+* S of rings and a subring s of R, subringMap e s is the induced equivalence between s and s.map e

                                                      Equations
                                                      • e.subringMap = e.subsemiringMap s.toSubsemiring
                                                      Instances For
                                                        theorem Subring.InClosure.recOn {R : Type u} [Ring R] {s : Set R} {C : RProp} {x : R} (hx : x Subring.closure s) (h1 : C 1) (hneg1 : C (-1)) (hs : zs, ∀ (n : R), C nC (z * n)) (ha : ∀ {x y : R}, C xC yC (x + y)) :
                                                        C x
                                                        theorem Subring.closure_preimage_le {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (s : Set S) :
                                                        theorem AddSubgroup.int_mul_mem {R : Type u} [Ring R] {G : AddSubgroup R} (k : ) {g : R} (h : g G) :
                                                        k * g G

                                                        Actions by Subrings #

                                                        These are just copies of the definitions about Subsemiring starting from Subsemiring.MulAction.

                                                        When R is commutative, Algebra.ofSubring provides a stronger result than those found in this file, which uses the same scalar action.

                                                        instance Subring.instSMulSubtypeMem {R : Type u} [Ring R] {α : Type u_1} [SMul R α] (S : Subring R) :
                                                        SMul (↥S) α

                                                        The action by a subring is the action by the underlying ring.

                                                        Equations
                                                        theorem Subring.smul_def {R : Type u} [Ring R] {α : Type u_1} [SMul R α] {S : Subring R} (g : S) (m : α) :
                                                        g m = g m
                                                        instance Subring.smulCommClass_left {R : Type u} [Ring R] {α : Type u_1} {β : Type u_2} [SMul R β] [SMul α β] [SMulCommClass R α β] (S : Subring R) :
                                                        SMulCommClass (↥S) α β
                                                        Equations
                                                        • =
                                                        instance Subring.smulCommClass_right {R : Type u} [Ring R] {α : Type u_1} {β : Type u_2} [SMul α β] [SMul R β] [SMulCommClass α R β] (S : Subring R) :
                                                        SMulCommClass α (↥S) β
                                                        Equations
                                                        • =
                                                        instance Subring.instIsScalarTowerSubtypeMem {R : Type u} [Ring R] {α : Type u_1} {β : Type u_2} [SMul α β] [SMul R α] [SMul R β] [IsScalarTower R α β] (S : Subring R) :
                                                        IsScalarTower (↥S) α β

                                                        Note that this provides IsScalarTower S R R which is needed by smul_mul_assoc.

                                                        Equations
                                                        • =
                                                        instance Subring.instFaithfulSMulSubtypeMem {R : Type u} [Ring R] {α : Type u_1} [SMul R α] [FaithfulSMul R α] (S : Subring R) :
                                                        FaithfulSMul (↥S) α
                                                        Equations
                                                        • =
                                                        instance Subring.instMulActionSubtypeMem {R : Type u} [Ring R] {α : Type u_1} [MulAction R α] (S : Subring R) :
                                                        MulAction (↥S) α

                                                        The action by a subring is the action by the underlying ring.

                                                        Equations
                                                        instance Subring.instDistribMulActionSubtypeMem {R : Type u} [Ring R] {α : Type u_1} [AddMonoid α] [DistribMulAction R α] (S : Subring R) :

                                                        The action by a subring is the action by the underlying ring.

                                                        Equations
                                                        instance Subring.instMulDistribMulActionSubtypeMem {R : Type u} [Ring R] {α : Type u_1} [Monoid α] [MulDistribMulAction R α] (S : Subring R) :

                                                        The action by a subring is the action by the underlying ring.

                                                        Equations
                                                        instance Subring.instSMulWithZeroSubtypeMem {R : Type u} [Ring R] {α : Type u_1} [Zero α] [SMulWithZero R α] (S : Subring R) :
                                                        SMulWithZero (↥S) α

                                                        The action by a subring is the action by the underlying ring.

                                                        Equations
                                                        instance Subring.instMulActionWithZeroSubtypeMem {R : Type u} [Ring R] {α : Type u_1} [Zero α] [MulActionWithZero R α] (S : Subring R) :

                                                        The action by a subring is the action by the underlying ring.

                                                        Equations
                                                        • S.instMulActionWithZeroSubtypeMem = S.mulActionWithZero
                                                        instance Subring.instModuleSubtypeMem {R : Type u} [Ring R] {α : Type u_1} [AddCommMonoid α] [Module R α] (S : Subring R) :
                                                        Module (↥S) α

                                                        The action by a subring is the action by the underlying ring.

                                                        Equations
                                                        • S.instModuleSubtypeMem = S.module
                                                        instance Subring.instMulSemiringActionSubtypeMem {R : Type u} [Ring R] {α : Type u_1} [Semiring α] [MulSemiringAction R α] (S : Subring R) :

                                                        The action by a subsemiring is the action by the underlying ring.

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                                                        The center of a semiring acts commutatively on that semiring.

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                                                        The center of a semiring acts commutatively on that semiring.

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                                                        theorem Subring.map_comap_eq {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (t : Subring S) :
                                                        Subring.map f (Subring.comap f t) = t f.range
                                                        theorem Subring.map_comap_eq_self {R : Type u} {S : Type v} [Ring R] [Ring S] {f : R →+* S} {t : Subring S} (h : t f.range) :
                                                        theorem Subring.map_comap_eq_self_of_surjective {R : Type u} {S : Type v} [Ring R] [Ring S] {f : R →+* S} (hf : Function.Surjective f) (t : Subring S) :
                                                        theorem Subring.comap_map_eq {R : Type u} {S : Type v} [Ring R] [Ring S] (f : R →+* S) (s : Subring R) :
                                                        theorem Subring.comap_map_eq_self {R : Type u} {S : Type v} [Ring R] [Ring S] {f : R →+* S} {s : Subring R} (h : f ⁻¹' {0} s) :
                                                        theorem Subring.comap_map_eq_self_of_injective {R : Type u} {S : Type v} [Ring R] [Ring S] {f : R →+* S} (hf : Function.Injective f) (s : Subring R) :