Documentation

Mathlib.Algebra.MonoidAlgebra.Defs

Monoid algebras #

When the domain of a Finsupp has a multiplicative or additive structure, we can define a convolution product. To mathematicians this structure is known as the "monoid algebra", i.e. the finite formal linear combinations over a given semiring of elements of the monoid. The "group ring" ℤ[G] or the "group algebra" k[G] are typical uses.

In fact the construction of the "monoid algebra" makes sense when G is not even a monoid, but merely a magma, i.e., when G carries a multiplication which is not required to satisfy any conditions at all. In this case the construction yields a not-necessarily-unital, not-necessarily-associative algebra but it is still adjoint to the forgetful functor from such algebras to magmas, and we prove this as MonoidAlgebra.liftMagma.

In this file we define MonoidAlgebra k G := G →₀ k, and AddMonoidAlgebra k G in the same way, and then define the convolution product on these.

When the domain is additive, this is used to define polynomials:

Polynomial R := AddMonoidAlgebra R ℕ
MvPolynomial σ α := AddMonoidAlgebra R (σ →₀ ℕ)

When the domain is multiplicative, e.g. a group, this will be used to define the group ring.

Notation #

We introduce the notation R[A] for AddMonoidAlgebra R A.

Implementation note #

Unfortunately because additive and multiplicative structures both appear in both cases, it doesn't appear to be possible to make much use of to_additive, and we just settle for saying everything twice.

Similarly, I attempted to just define k[G] := MonoidAlgebra k (Multiplicative G), but the definitional equality Multiplicative G = G leaks through everywhere, and seems impossible to use.

Multiplicative monoids #

def MonoidAlgebra (k : Type u₁) (G : Type u₂) [Semiring k] :
Type (max u₁ u₂)

The monoid algebra over a semiring k generated by the monoid G. It is the type of finite formal k-linear combinations of terms of G, endowed with the convolution product.

Equations
Instances For
    Equations
    • =
    instance MonoidAlgebra.coeFun (k : Type u₁) (G : Type u₂) [Semiring k] :
    CoeFun (MonoidAlgebra k G) fun (x : MonoidAlgebra k G) => Gk
    Equations
    @[reducible, inline]
    abbrev MonoidAlgebra.single {k : Type u₁} {G : Type u₂} [Semiring k] (a : G) (b : k) :
    Equations
    Instances For
      theorem MonoidAlgebra.single_zero {k : Type u₁} {G : Type u₂} [Semiring k] (a : G) :
      theorem MonoidAlgebra.single_add {k : Type u₁} {G : Type u₂} [Semiring k] (a : G) (b₁ : k) (b₂ : k) :
      @[simp]
      theorem MonoidAlgebra.sum_single_index {k : Type u₁} {G : Type u₂} [Semiring k] {N : Type u_3} [AddCommMonoid N] {a : G} {b : k} {h : GkN} (h_zero : h a 0 = 0) :
      @[simp]
      theorem MonoidAlgebra.sum_single {k : Type u₁} {G : Type u₂} [Semiring k] (f : MonoidAlgebra k G) :
      Finsupp.sum f MonoidAlgebra.single = f
      theorem MonoidAlgebra.single_apply {k : Type u₁} {G : Type u₂} [Semiring k] {a : G} {a' : G} {b : k} [Decidable (a = a')] :
      (MonoidAlgebra.single a b) a' = if a = a' then b else 0
      @[simp]
      theorem MonoidAlgebra.single_eq_zero {k : Type u₁} {G : Type u₂} [Semiring k] {a : G} {b : k} :
      @[reducible, inline]
      abbrev MonoidAlgebra.mapDomain {k : Type u₁} {G : Type u₂} [Semiring k] {G' : Type u_3} (f : GG') (v : MonoidAlgebra k G) :
      Equations
      Instances For
        theorem MonoidAlgebra.mapDomain_sum {k : Type u₁} {G : Type u₂} [Semiring k] {k' : Type u_3} {G' : Type u_4} [Semiring k'] {f : GG'} {s : MonoidAlgebra k' G} {v : Gk'MonoidAlgebra k G} :
        MonoidAlgebra.mapDomain f (Finsupp.sum s v) = Finsupp.sum s fun (a : G) (b : k') => MonoidAlgebra.mapDomain f (v a b)
        def MonoidAlgebra.liftNC {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [NonUnitalNonAssocSemiring R] (f : k →+ R) (g : GR) :

        A non-commutative version of MonoidAlgebra.lift: given an additive homomorphism f : k →+ R and a homomorphism g : G → R, returns the additive homomorphism from MonoidAlgebra k G such that liftNC f g (single a b) = f b * g a. If f is a ring homomorphism and the range of either f or g is in center of R, then the result is a ring homomorphism. If R is a k-algebra and f = algebraMap k R, then the result is an algebra homomorphism called MonoidAlgebra.lift.

        Equations
        Instances For
          @[simp]
          theorem MonoidAlgebra.liftNC_single {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [NonUnitalNonAssocSemiring R] (f : k →+ R) (g : GR) (a : G) (b : k) :
          @[irreducible]
          def MonoidAlgebra.mul' {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] (f : MonoidAlgebra k G) (g : MonoidAlgebra k G) :

          The multiplication in a monoid algebra. We make it irreducible so that Lean doesn't unfold it trying to unify two things that are different.

          Equations
          Instances For
            instance MonoidAlgebra.instMul {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] :

            The product of f g : MonoidAlgebra k G is the finitely supported function whose value at a is the sum of f x * g y over all pairs x, y such that x * y = a. (Think of the group ring of a group.)

            Equations
            • MonoidAlgebra.instMul = { mul := MonoidAlgebra.mul' }
            theorem MonoidAlgebra.mul_def {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] {f : MonoidAlgebra k G} {g : MonoidAlgebra k G} :
            f * g = Finsupp.sum f fun (a₁ : G) (b₁ : k) => Finsupp.sum g fun (a₂ : G) (b₂ : k) => MonoidAlgebra.single (a₁ * a₂) (b₁ * b₂)
            Equations
            theorem MonoidAlgebra.liftNC_mul {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [Mul G] [Semiring R] {g_hom : Type u_3} [FunLike g_hom G R] [MulHomClass g_hom G R] (f : k →+* R) (g : g_hom) (a : MonoidAlgebra k G) (b : MonoidAlgebra k G) (h_comm : ∀ {x y : G}, y a.supportCommute (f (b x)) (g y)) :
            (MonoidAlgebra.liftNC f g) (a * b) = (MonoidAlgebra.liftNC f g) a * (MonoidAlgebra.liftNC f g) b
            Equations
            instance MonoidAlgebra.one {k : Type u₁} {G : Type u₂} [Semiring k] [One G] :

            The unit of the multiplication is single 1 1, i.e. the function that is 1 at 1 and zero elsewhere.

            Equations
            theorem MonoidAlgebra.one_def {k : Type u₁} {G : Type u₂} [Semiring k] [One G] :
            @[simp]
            theorem MonoidAlgebra.liftNC_one {k : Type u₁} {G : Type u₂} {R : Type u_2} [NonAssocSemiring R] [Semiring k] [One G] {g_hom : Type u_3} [FunLike g_hom G R] [OneHomClass g_hom G R] (f : k →+* R) (g : g_hom) :
            (MonoidAlgebra.liftNC f g) 1 = 1
            Equations
            theorem MonoidAlgebra.natCast_def {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] (n : ) :
            @[deprecated MonoidAlgebra.natCast_def]
            theorem MonoidAlgebra.nat_cast_def {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] (n : ) :

            Alias of MonoidAlgebra.natCast_def.

            Semiring structure #

            instance MonoidAlgebra.semiring {k : Type u₁} {G : Type u₂} [Semiring k] [Monoid G] :
            Equations
            • MonoidAlgebra.semiring = Semiring.mk npowRec
            def MonoidAlgebra.liftNCRingHom {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [Monoid G] [Semiring R] (f : k →+* R) (g : G →* R) (h_comm : ∀ (x : k) (y : G), Commute (f x) (g y)) :

            liftNC as a RingHom, for when f x and g y commute

            Equations
            Instances For
              Equations
              instance MonoidAlgebra.nontrivial {k : Type u₁} {G : Type u₂} [Semiring k] [Nontrivial k] [Nonempty G] :
              Equations
              • =

              Derived instances #

              Equations
              instance MonoidAlgebra.unique {k : Type u₁} {G : Type u₂} [Semiring k] [Subsingleton k] :
              Equations
              • MonoidAlgebra.unique = Finsupp.uniqueOfRight
              instance MonoidAlgebra.addCommGroup {k : Type u₁} {G : Type u₂} [Ring k] :
              Equations
              • MonoidAlgebra.addCommGroup = Finsupp.instAddCommGroup
              Equations
              instance MonoidAlgebra.nonUnitalRing {k : Type u₁} {G : Type u₂} [Ring k] [Semigroup G] :
              Equations
              instance MonoidAlgebra.nonAssocRing {k : Type u₁} {G : Type u₂} [Ring k] [MulOneClass G] :
              Equations
              theorem MonoidAlgebra.intCast_def {k : Type u₁} {G : Type u₂} [Ring k] [MulOneClass G] (z : ) :
              @[deprecated MonoidAlgebra.intCast_def]
              theorem MonoidAlgebra.int_cast_def {k : Type u₁} {G : Type u₂} [Ring k] [MulOneClass G] (z : ) :

              Alias of MonoidAlgebra.intCast_def.

              instance MonoidAlgebra.ring {k : Type u₁} {G : Type u₂} [Ring k] [Monoid G] :
              Equations
              • MonoidAlgebra.ring = Ring.mk SubNegMonoid.zsmul
              Equations
              instance MonoidAlgebra.commRing {k : Type u₁} {G : Type u₂} [CommRing k] [CommMonoid G] :
              Equations
              instance MonoidAlgebra.smulZeroClass {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [SMulZeroClass R k] :
              Equations
              • MonoidAlgebra.smulZeroClass = Finsupp.smulZeroClass
              instance MonoidAlgebra.distribSMul {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [DistribSMul R k] :
              Equations
              instance MonoidAlgebra.distribMulAction {k : Type u₁} {G : Type u₂} {R : Type u_2} [Monoid R] [Semiring k] [DistribMulAction R k] :
              Equations
              instance MonoidAlgebra.module {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring R] [Semiring k] [Module R k] :
              Equations
              instance MonoidAlgebra.faithfulSMul {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [SMulZeroClass R k] [FaithfulSMul R k] [Nonempty G] :
              Equations
              • =
              instance MonoidAlgebra.isScalarTower {k : Type u₁} {G : Type u₂} {R : Type u_2} {S : Type u_3} [Semiring k] [SMulZeroClass R k] [SMulZeroClass S k] [SMul R S] [IsScalarTower R S k] :
              Equations
              • =
              instance MonoidAlgebra.smulCommClass {k : Type u₁} {G : Type u₂} {R : Type u_2} {S : Type u_3} [Semiring k] [SMulZeroClass R k] [SMulZeroClass S k] [SMulCommClass R S k] :
              Equations
              • =
              Equations
              • =

              This is not an instance as it conflicts with MonoidAlgebra.distribMulAction when G = kˣ.

              Equations
              • MonoidAlgebra.comapDistribMulActionSelf = Finsupp.comapDistribMulAction
              Instances For
                theorem MonoidAlgebra.mul_apply {k : Type u₁} {G : Type u₂} [Semiring k] [DecidableEq G] [Mul G] (f : MonoidAlgebra k G) (g : MonoidAlgebra k G) (x : G) :
                (f * g) x = Finsupp.sum f fun (a₁ : G) (b₁ : k) => Finsupp.sum g fun (a₂ : G) (b₂ : k) => if a₁ * a₂ = x then b₁ * b₂ else 0
                theorem MonoidAlgebra.mul_apply_antidiagonal {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] (f : MonoidAlgebra k G) (g : MonoidAlgebra k G) (x : G) (s : Finset (G × G)) (hs : ∀ {p : G × G}, p s p.1 * p.2 = x) :
                (f * g) x = ps, f p.1 * g p.2
                @[simp]
                theorem MonoidAlgebra.single_mul_single {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] {a₁ : G} {a₂ : G} {b₁ : k} {b₂ : k} :
                MonoidAlgebra.single a₁ b₁ * MonoidAlgebra.single a₂ b₂ = MonoidAlgebra.single (a₁ * a₂) (b₁ * b₂)
                theorem MonoidAlgebra.single_commute_single {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] {a₁ : G} {a₂ : G} {b₁ : k} {b₂ : k} (ha : Commute a₁ a₂) (hb : Commute b₁ b₂) :
                theorem MonoidAlgebra.single_commute {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] {a : G} {b : k} (ha : ∀ (a' : G), Commute a a') (hb : ∀ (b' : k), Commute b b') (f : MonoidAlgebra k G) :
                @[simp]
                theorem MonoidAlgebra.single_pow {k : Type u₁} {G : Type u₂} [Semiring k] [Monoid G] {a : G} {b : k} (n : ) :
                @[simp]
                theorem MonoidAlgebra.mapDomain_one {α : Type u_3} {β : Type u_4} {α₂ : Type u_5} [Semiring β] [One α] [One α₂] {F : Type u_6} [FunLike F α α₂] [OneHomClass F α α₂] (f : F) :

                Like Finsupp.mapDomain_zero, but for the 1 we define in this file

                theorem MonoidAlgebra.mapDomain_mul {α : Type u_3} {β : Type u_4} {α₂ : Type u_5} [Semiring β] [Mul α] [Mul α₂] {F : Type u_6} [FunLike F α α₂] [MulHomClass F α α₂] (f : F) (x : MonoidAlgebra β α) (y : MonoidAlgebra β α) :

                Like Finsupp.mapDomain_add, but for the convolutive multiplication we define in this file

                @[simp]
                theorem MonoidAlgebra.ofMagma_apply (k : Type u₁) (G : Type u₂) [Semiring k] [Mul G] (a : G) :
                def MonoidAlgebra.ofMagma (k : Type u₁) (G : Type u₂) [Semiring k] [Mul G] :

                The embedding of a magma into its magma algebra.

                Equations
                Instances For
                  @[simp]
                  theorem MonoidAlgebra.of_apply (k : Type u₁) (G : Type u₂) [Semiring k] [MulOneClass G] (a : G) :
                  def MonoidAlgebra.of (k : Type u₁) (G : Type u₂) [Semiring k] [MulOneClass G] :

                  The embedding of a unital magma into its magma algebra.

                  Equations
                  Instances For
                    theorem MonoidAlgebra.smul_of {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] (g : G) (r : k) :
                    theorem MonoidAlgebra.of_commute {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] {a : G} (h : ∀ (a' : G), Commute a a') (f : MonoidAlgebra k G) :
                    @[simp]
                    theorem MonoidAlgebra.singleHom_apply {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] (a : k × G) :
                    MonoidAlgebra.singleHom a = MonoidAlgebra.single a.2 a.1
                    def MonoidAlgebra.singleHom {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] :

                    Finsupp.single as a MonoidHom from the product type into the monoid algebra.

                    Note the order of the elements of the product are reversed compared to the arguments of Finsupp.single.

                    Equations
                    • MonoidAlgebra.singleHom = { toFun := fun (a : k × G) => MonoidAlgebra.single a.2 a.1, map_one' := , map_mul' := }
                    Instances For
                      theorem MonoidAlgebra.mul_single_apply_aux {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] (f : MonoidAlgebra k G) {r : k} {x : G} {y : G} {z : G} (H : ∀ (a : G), a * x = z a = y) :
                      (f * MonoidAlgebra.single x r) z = f y * r
                      theorem MonoidAlgebra.mul_single_one_apply {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] (f : MonoidAlgebra k G) (r : k) (x : G) :
                      (f * MonoidAlgebra.single 1 r) x = f x * r
                      theorem MonoidAlgebra.mul_single_apply_of_not_exists_mul {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] (r : k) {g : G} {g' : G} (x : MonoidAlgebra k G) (h : ¬∃ (d : G), g' = d * g) :
                      (x * MonoidAlgebra.single g r) g' = 0
                      theorem MonoidAlgebra.single_mul_apply_aux {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] (f : MonoidAlgebra k G) {r : k} {x : G} {y : G} {z : G} (H : ∀ (a : G), x * a = y a = z) :
                      (MonoidAlgebra.single x r * f) y = r * f z
                      theorem MonoidAlgebra.single_one_mul_apply {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] (f : MonoidAlgebra k G) (r : k) (x : G) :
                      (MonoidAlgebra.single 1 r * f) x = r * f x
                      theorem MonoidAlgebra.single_mul_apply_of_not_exists_mul {k : Type u₁} {G : Type u₂} [Semiring k] [Mul G] (r : k) {g : G} {g' : G} (x : MonoidAlgebra k G) (h : ¬∃ (d : G), g' = g * d) :
                      (MonoidAlgebra.single g r * x) g' = 0
                      theorem MonoidAlgebra.liftNC_smul {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] {R : Type u_3} [Semiring R] (f : k →+* R) (g : G →* R) (c : k) (φ : MonoidAlgebra k G) :
                      (MonoidAlgebra.liftNC f g) (c φ) = f c * (MonoidAlgebra.liftNC f g) φ

                      Non-unital, non-associative algebra structure #

                      instance MonoidAlgebra.isScalarTower_self (k : Type u₁) {G : Type u₂} {R : Type u_2} [Semiring k] [DistribSMul R k] [Mul G] [IsScalarTower R k k] :
                      Equations
                      • =
                      instance MonoidAlgebra.smulCommClass_self (k : Type u₁) {G : Type u₂} {R : Type u_2} [Semiring k] [DistribSMul R k] [Mul G] [SMulCommClass R k k] :

                      Note that if k is a CommSemiring then we have SMulCommClass k k k and so we can take R = k in the below. In other words, if the coefficients are commutative amongst themselves, they also commute with the algebra multiplication.

                      Equations
                      • =
                      instance MonoidAlgebra.smulCommClass_symm_self (k : Type u₁) {G : Type u₂} {R : Type u_2} [Semiring k] [DistribSMul R k] [Mul G] [SMulCommClass k R k] :
                      Equations
                      • =
                      @[simp]
                      theorem MonoidAlgebra.singleOneRingHom_apply {k : Type u₁} {G : Type u₂} [Semiring k] [MulOneClass G] :
                      ∀ (a : k), MonoidAlgebra.singleOneRingHom a = (↑(Finsupp.singleAddHom 1)).toFun a

                      Finsupp.single 1 as a RingHom

                      Equations
                      • MonoidAlgebra.singleOneRingHom = { toFun := (↑(Finsupp.singleAddHom 1)).toFun, map_one' := , map_mul' := , map_zero' := , map_add' := }
                      Instances For
                        @[simp]
                        theorem MonoidAlgebra.mapDomainRingHom_apply {G : Type u₂} (k : Type u_3) {H : Type u_4} {F : Type u_5} [Semiring k] [Monoid G] [Monoid H] [FunLike F G H] [MonoidHomClass F G H] (f : F) :
                        ∀ (a : G →₀ k), (MonoidAlgebra.mapDomainRingHom k f) a = (↑(Finsupp.mapDomain.addMonoidHom f)).toFun a
                        def MonoidAlgebra.mapDomainRingHom {G : Type u₂} (k : Type u_3) {H : Type u_4} {F : Type u_5} [Semiring k] [Monoid G] [Monoid H] [FunLike F G H] [MonoidHomClass F G H] (f : F) :

                        If f : G → H is a multiplicative homomorphism between two monoids, then Finsupp.mapDomain f is a ring homomorphism between their monoid algebras.

                        Equations
                        Instances For
                          theorem MonoidAlgebra.ringHom_ext {k : Type u₁} {G : Type u₂} {R : Type u_3} [Semiring k] [MulOneClass G] [Semiring R] {f : MonoidAlgebra k G →+* R} {g : MonoidAlgebra k G →+* R} (h₁ : ∀ (b : k), f (MonoidAlgebra.single 1 b) = g (MonoidAlgebra.single 1 b)) (h_of : ∀ (a : G), f (MonoidAlgebra.single a 1) = g (MonoidAlgebra.single a 1)) :
                          f = g

                          If two ring homomorphisms from MonoidAlgebra k G are equal on all single a 1 and single 1 b, then they are equal.

                          theorem MonoidAlgebra.ringHom_ext'_iff {k : Type u₁} {G : Type u₂} {R : Type u_3} [Semiring k] [MulOneClass G] [Semiring R] {f : MonoidAlgebra k G →+* R} {g : MonoidAlgebra k G →+* R} :
                          f = g f.comp MonoidAlgebra.singleOneRingHom = g.comp MonoidAlgebra.singleOneRingHom (↑f).comp (MonoidAlgebra.of k G) = (↑g).comp (MonoidAlgebra.of k G)
                          theorem MonoidAlgebra.ringHom_ext' {k : Type u₁} {G : Type u₂} {R : Type u_3} [Semiring k] [MulOneClass G] [Semiring R] {f : MonoidAlgebra k G →+* R} {g : MonoidAlgebra k G →+* R} (h₁ : f.comp MonoidAlgebra.singleOneRingHom = g.comp MonoidAlgebra.singleOneRingHom) (h_of : (↑f).comp (MonoidAlgebra.of k G) = (↑g).comp (MonoidAlgebra.of k G)) :
                          f = g

                          If two ring homomorphisms from MonoidAlgebra k G are equal on all single a 1 and single 1 b, then they are equal.

                          See note [partially-applied ext lemmas].

                          theorem MonoidAlgebra.induction_on {k : Type u₁} {G : Type u₂} [Semiring k] [Monoid G] {p : MonoidAlgebra k GProp} (f : MonoidAlgebra k G) (hM : ∀ (g : G), p ((MonoidAlgebra.of k G) g)) (hadd : ∀ (f g : MonoidAlgebra k G), p fp gp (f + g)) (hsmul : ∀ (r : k) (f : MonoidAlgebra k G), p fp (r f)) :
                          p f
                          theorem MonoidAlgebra.prod_single {k : Type u₁} {G : Type u₂} {ι : Type ui} [CommSemiring k] [CommMonoid G] {s : Finset ι} {a : ιG} {b : ιk} :
                          is, MonoidAlgebra.single (a i) (b i) = MonoidAlgebra.single (∏ is, a i) (∏ is, b i)
                          @[simp]
                          theorem MonoidAlgebra.mul_single_apply {k : Type u₁} {G : Type u₂} [Semiring k] [Group G] (f : MonoidAlgebra k G) (r : k) (x : G) (y : G) :
                          (f * MonoidAlgebra.single x r) y = f (y * x⁻¹) * r
                          @[simp]
                          theorem MonoidAlgebra.single_mul_apply {k : Type u₁} {G : Type u₂} [Semiring k] [Group G] (r : k) (x : G) (f : MonoidAlgebra k G) (y : G) :
                          (MonoidAlgebra.single x r * f) y = r * f (x⁻¹ * y)
                          theorem MonoidAlgebra.mul_apply_left {k : Type u₁} {G : Type u₂} [Semiring k] [Group G] (f : MonoidAlgebra k G) (g : MonoidAlgebra k G) (x : G) :
                          (f * g) x = Finsupp.sum f fun (a : G) (b : k) => b * g (a⁻¹ * x)
                          theorem MonoidAlgebra.mul_apply_right {k : Type u₁} {G : Type u₂} [Semiring k] [Group G] (f : MonoidAlgebra k G) (g : MonoidAlgebra k G) (x : G) :
                          (f * g) x = Finsupp.sum g fun (a : G) (b : k) => f (x * a⁻¹) * b
                          @[simp]
                          theorem MonoidAlgebra.opRingEquiv_apply {k : Type u₁} {G : Type u₂} [Semiring k] [Monoid G] :
                          ∀ (a : (G →₀ k)ᵐᵒᵖ), MonoidAlgebra.opRingEquiv a = Finsupp.equivMapDomain MulOpposite.opEquiv (Finsupp.mapRange MulOpposite.op (MulOpposite.unop a))
                          @[simp]
                          theorem MonoidAlgebra.opRingEquiv_symm_apply {k : Type u₁} {G : Type u₂} [Semiring k] [Monoid G] :
                          ∀ (a : Gᵐᵒᵖ →₀ kᵐᵒᵖ), MonoidAlgebra.opRingEquiv.symm a = MulOpposite.op (Finsupp.mapRange MulOpposite.unop (Finsupp.equivMapDomain MulOpposite.opEquiv.symm a))

                          The opposite of a MonoidAlgebra R I equivalent as a ring to the MonoidAlgebra Rᵐᵒᵖ Iᵐᵒᵖ over the opposite ring, taking elements to their opposite.

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                            theorem MonoidAlgebra.opRingEquiv_single {k : Type u₁} {G : Type u₂} [Semiring k] [Monoid G] (r : k) (x : G) :
                            def MonoidAlgebra.submoduleOfSMulMem {k : Type u₁} {G : Type u₂} [CommSemiring k] [Monoid G] {V : Type u_3} [AddCommMonoid V] [Module k V] [Module (MonoidAlgebra k G) V] [IsScalarTower k (MonoidAlgebra k G) V] (W : Submodule k V) (h : ∀ (g : G), vW, (MonoidAlgebra.of k G) g v W) :

                            A submodule over k which is stable under scalar multiplication by elements of G is a submodule over MonoidAlgebra k G

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                              Additive monoids #

                              def AddMonoidAlgebra (k : Type u₁) (G : Type u₂) [Semiring k] :
                              Type (max u₂ u₁)

                              The monoid algebra over a semiring k generated by the additive monoid G. It is the type of finite formal k-linear combinations of terms of G, endowed with the convolution product.

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                                The monoid algebra over a semiring k generated by the additive monoid G. It is the type of finite formal k-linear combinations of terms of G, endowed with the convolution product.

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                                • One or more equations did not get rendered due to their size.
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                                  instance AddMonoidAlgebra.coeFun (k : Type u₁) (G : Type u₂) [Semiring k] :
                                  CoeFun (AddMonoidAlgebra k G) fun (x : AddMonoidAlgebra k G) => Gk
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                                  @[reducible, inline]
                                  abbrev AddMonoidAlgebra.single {k : Type u₁} {G : Type u₂} [Semiring k] (a : G) (b : k) :
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                                    theorem AddMonoidAlgebra.single_zero {k : Type u₁} {G : Type u₂} [Semiring k] (a : G) :
                                    theorem AddMonoidAlgebra.single_add {k : Type u₁} {G : Type u₂} [Semiring k] (a : G) (b₁ : k) (b₂ : k) :
                                    @[simp]
                                    theorem AddMonoidAlgebra.sum_single_index {k : Type u₁} {G : Type u₂} [Semiring k] {N : Type u_3} [AddCommMonoid N] {a : G} {b : k} {h : GkN} (h_zero : h a 0 = 0) :
                                    @[simp]
                                    theorem AddMonoidAlgebra.sum_single {k : Type u₁} {G : Type u₂} [Semiring k] (f : AddMonoidAlgebra k G) :
                                    Finsupp.sum f AddMonoidAlgebra.single = f
                                    theorem AddMonoidAlgebra.single_apply {k : Type u₁} {G : Type u₂} [Semiring k] {a : G} {a' : G} {b : k} [Decidable (a = a')] :
                                    (AddMonoidAlgebra.single a b) a' = if a = a' then b else 0
                                    @[simp]
                                    theorem AddMonoidAlgebra.single_eq_zero {k : Type u₁} {G : Type u₂} [Semiring k] {a : G} {b : k} :
                                    @[reducible, inline]
                                    abbrev AddMonoidAlgebra.mapDomain {k : Type u₁} {G : Type u₂} [Semiring k] {G' : Type u_3} (f : GG') (v : AddMonoidAlgebra k G) :
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                                      theorem AddMonoidAlgebra.mapDomain_sum {k : Type u₁} {G : Type u₂} [Semiring k] {k' : Type u_3} {G' : Type u_4} [Semiring k'] {f : GG'} {s : AddMonoidAlgebra k' G} {v : Gk'AddMonoidAlgebra k G} :
                                      theorem AddMonoidAlgebra.mapDomain_single {k : Type u₁} {G : Type u₂} [Semiring k] {G' : Type u_3} {f : GG'} {a : G} {b : k} :
                                      def AddMonoidAlgebra.liftNC {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [NonUnitalNonAssocSemiring R] (f : k →+ R) (g : Multiplicative GR) :

                                      A non-commutative version of AddMonoidAlgebra.lift: given an additive homomorphism f : k →+ R and a map g : Multiplicative G → R, returns the additive homomorphism from k[G] such that liftNC f g (single a b) = f b * g a. If f is a ring homomorphism and the range of either f or g is in center of R, then the result is a ring homomorphism. If R is a k-algebra and f = algebraMap k R, then the result is an algebra homomorphism called AddMonoidAlgebra.lift.

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                                        @[simp]
                                        theorem AddMonoidAlgebra.liftNC_single {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [NonUnitalNonAssocSemiring R] (f : k →+ R) (g : Multiplicative GR) (a : G) (b : k) :
                                        (AddMonoidAlgebra.liftNC f g) (AddMonoidAlgebra.single a b) = f b * g (Multiplicative.ofAdd a)
                                        instance AddMonoidAlgebra.hasMul {k : Type u₁} {G : Type u₂} [Semiring k] [Add G] :

                                        The product of f g : k[G] is the finitely supported function whose value at a is the sum of f x * g y over all pairs x, y such that x + y = a. (Think of the product of multivariate polynomials where α is the additive monoid of monomial exponents.)

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                                        theorem AddMonoidAlgebra.mul_def {k : Type u₁} {G : Type u₂} [Semiring k] [Add G] {f : AddMonoidAlgebra k G} {g : AddMonoidAlgebra k G} :
                                        f * g = Finsupp.sum f fun (a₁ : G) (b₁ : k) => Finsupp.sum g fun (a₂ : G) (b₂ : k) => AddMonoidAlgebra.single (a₁ + a₂) (b₁ * b₂)
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                                        theorem AddMonoidAlgebra.liftNC_mul {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [Add G] [Semiring R] {g_hom : Type u_3} [FunLike g_hom (Multiplicative G) R] [MulHomClass g_hom (Multiplicative G) R] (f : k →+* R) (g : g_hom) (a : AddMonoidAlgebra k G) (b : AddMonoidAlgebra k G) (h_comm : ∀ {x y : G}, y a.supportCommute (f (b x)) (g (Multiplicative.ofAdd y))) :
                                        (AddMonoidAlgebra.liftNC f g) (a * b) = (AddMonoidAlgebra.liftNC f g) a * (AddMonoidAlgebra.liftNC f g) b
                                        instance AddMonoidAlgebra.one {k : Type u₁} {G : Type u₂} [Semiring k] [Zero G] :

                                        The unit of the multiplication is single 0 1, i.e. the function that is 1 at 0 and zero elsewhere.

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                                        theorem AddMonoidAlgebra.one_def {k : Type u₁} {G : Type u₂} [Semiring k] [Zero G] :
                                        @[simp]
                                        theorem AddMonoidAlgebra.liftNC_one {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [Zero G] [NonAssocSemiring R] {g_hom : Type u_3} [FunLike g_hom (Multiplicative G) R] [OneHomClass g_hom (Multiplicative G) R] (f : k →+* R) (g : g_hom) :
                                        (AddMonoidAlgebra.liftNC f g) 1 = 1
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                                        theorem AddMonoidAlgebra.natCast_def {k : Type u₁} {G : Type u₂} [Semiring k] [AddZeroClass G] (n : ) :
                                        @[deprecated AddMonoidAlgebra.natCast_def]
                                        theorem AddMonoidAlgebra.nat_cast_def {k : Type u₁} {G : Type u₂} [Semiring k] [AddZeroClass G] (n : ) :

                                        Alias of AddMonoidAlgebra.natCast_def.

                                        Semiring structure #

                                        instance AddMonoidAlgebra.smulZeroClass {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [SMulZeroClass R k] :
                                        Equations
                                        • AddMonoidAlgebra.smulZeroClass = Finsupp.smulZeroClass
                                        instance AddMonoidAlgebra.semiring {k : Type u₁} {G : Type u₂} [Semiring k] [AddMonoid G] :
                                        Equations
                                        • AddMonoidAlgebra.semiring = Semiring.mk npowRec
                                        def AddMonoidAlgebra.liftNCRingHom {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [AddMonoid G] [Semiring R] (f : k →+* R) (g : Multiplicative G →* R) (h_comm : ∀ (x : k) (y : Multiplicative G), Commute (f x) (g y)) :

                                        liftNC as a RingHom, for when f and g commute

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                                          Derived instances #

                                          Equations
                                          instance AddMonoidAlgebra.unique {k : Type u₁} {G : Type u₂} [Semiring k] [Subsingleton k] :
                                          Equations
                                          • AddMonoidAlgebra.unique = Finsupp.uniqueOfRight
                                          instance AddMonoidAlgebra.addCommGroup {k : Type u₁} {G : Type u₂} [Ring k] :
                                          Equations
                                          • AddMonoidAlgebra.addCommGroup = Finsupp.instAddCommGroup
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                                          theorem AddMonoidAlgebra.intCast_def {k : Type u₁} {G : Type u₂} [Ring k] [AddZeroClass G] (z : ) :
                                          @[deprecated AddMonoidAlgebra.intCast_def]
                                          theorem AddMonoidAlgebra.int_cast_def {k : Type u₁} {G : Type u₂} [Ring k] [AddZeroClass G] (z : ) :

                                          Alias of AddMonoidAlgebra.intCast_def.

                                          instance AddMonoidAlgebra.ring {k : Type u₁} {G : Type u₂} [Ring k] [AddMonoid G] :
                                          Equations
                                          • AddMonoidAlgebra.ring = Ring.mk SubNegMonoid.zsmul
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                                          instance AddMonoidAlgebra.commRing {k : Type u₁} {G : Type u₂} [CommRing k] [AddCommMonoid G] :
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                                          instance AddMonoidAlgebra.distribSMul {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [DistribSMul R k] :
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                                          instance AddMonoidAlgebra.distribMulAction {k : Type u₁} {G : Type u₂} {R : Type u_2} [Monoid R] [Semiring k] [DistribMulAction R k] :
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                                          instance AddMonoidAlgebra.faithfulSMul {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring k] [SMulZeroClass R k] [FaithfulSMul R k] [Nonempty G] :
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                                          instance AddMonoidAlgebra.module {k : Type u₁} {G : Type u₂} {R : Type u_2} [Semiring R] [Semiring k] [Module R k] :
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                                          instance AddMonoidAlgebra.isScalarTower {k : Type u₁} {G : Type u₂} {R : Type u_2} {S : Type u_3} [Semiring k] [SMulZeroClass R k] [SMulZeroClass S k] [SMul R S] [IsScalarTower R S k] :
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                                          instance AddMonoidAlgebra.smulCommClass {k : Type u₁} {G : Type u₂} {R : Type u_2} {S : Type u_3} [Semiring k] [SMulZeroClass R k] [SMulZeroClass S k] [SMulCommClass R S k] :
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                                          It is hard to state the equivalent of DistribMulAction G k[G] because we've never discussed actions of additive groups.

                                          theorem AddMonoidAlgebra.mul_apply {k : Type u₁} {G : Type u₂} [Semiring k] [DecidableEq G] [Add G] (f : AddMonoidAlgebra k G) (g : AddMonoidAlgebra k G) (x : G) :
                                          (f * g) x = Finsupp.sum f fun (a₁ : G) (b₁ : k) => Finsupp.sum g fun (a₂ : G) (b₂ : k) => if a₁ + a₂ = x then b₁ * b₂ else 0
                                          theorem AddMonoidAlgebra.mul_apply_antidiagonal {k : Type u₁} {G : Type u₂} [Semiring k] [Add G] (f : AddMonoidAlgebra k G) (g : AddMonoidAlgebra k G) (x : G) (s : Finset (G × G)) (hs : ∀ {p : G × G}, p s p.1 + p.2 = x) :
                                          (f * g) x = ps, f p.1 * g p.2
                                          theorem AddMonoidAlgebra.single_mul_single {k : Type u₁} {G : Type u₂} [Semiring k] [Add G] {a₁ : G} {a₂ : G} {b₁ : k} {b₂ : k} :
                                          AddMonoidAlgebra.single a₁ b₁ * AddMonoidAlgebra.single a₂ b₂ = AddMonoidAlgebra.single (a₁ + a₂) (b₁ * b₂)
                                          theorem AddMonoidAlgebra.single_commute_single {k : Type u₁} {G : Type u₂} [Semiring k] [Add G] {a₁ : G} {a₂ : G} {b₁ : k} {b₂ : k} (ha : AddCommute a₁ a₂) (hb : Commute b₁ b₂) :
                                          theorem AddMonoidAlgebra.single_pow {k : Type u₁} {G : Type u₂} [Semiring k] [AddMonoid G] {a : G} {b : k} (n : ) :
                                          @[simp]
                                          theorem AddMonoidAlgebra.mapDomain_one {α : Type u_3} {β : Type u_4} {α₂ : Type u_5} [Semiring β] [Zero α] [Zero α₂] {F : Type u_6} [FunLike F α α₂] [ZeroHomClass F α α₂] (f : F) :

                                          Like Finsupp.mapDomain_zero, but for the 1 we define in this file

                                          theorem AddMonoidAlgebra.mapDomain_mul {α : Type u_3} {β : Type u_4} {α₂ : Type u_5} [Semiring β] [Add α] [Add α₂] {F : Type u_6} [FunLike F α α₂] [AddHomClass F α α₂] (f : F) (x : AddMonoidAlgebra β α) (y : AddMonoidAlgebra β α) :

                                          Like Finsupp.mapDomain_add, but for the convolutive multiplication we define in this file

                                          The embedding of an additive magma into its additive magma algebra.

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                                            Embedding of a magma with zero into its magma algebra.

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                                              def AddMonoidAlgebra.of' (k : Type u₁) (G : Type u₂) [Semiring k] :

                                              Embedding of a magma with zero G, into its magma algebra, having G as source.

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                                                @[simp]
                                                theorem AddMonoidAlgebra.of_apply {k : Type u₁} {G : Type u₂} [Semiring k] [AddZeroClass G] (a : Multiplicative G) :
                                                (AddMonoidAlgebra.of k G) a = AddMonoidAlgebra.single (Multiplicative.toAdd a) 1
                                                @[simp]
                                                theorem AddMonoidAlgebra.of'_apply {k : Type u₁} {G : Type u₂} [Semiring k] (a : G) :
                                                theorem AddMonoidAlgebra.of'_eq_of {k : Type u₁} {G : Type u₂} [Semiring k] [AddZeroClass G] (a : G) :
                                                AddMonoidAlgebra.of' k G a = (AddMonoidAlgebra.of k G) (Multiplicative.ofAdd a)
                                                theorem AddMonoidAlgebra.of'_commute {k : Type u₁} {G : Type u₂} [Semiring k] [AddZeroClass G] {a : G} (h : ∀ (a' : G), AddCommute a a') (f : AddMonoidAlgebra k G) :
                                                @[simp]
                                                theorem AddMonoidAlgebra.singleHom_apply {k : Type u₁} {G : Type u₂} [Semiring k] [AddZeroClass G] (a : k × Multiplicative G) :
                                                AddMonoidAlgebra.singleHom a = AddMonoidAlgebra.single (Multiplicative.toAdd a.2) a.1

                                                Finsupp.single as a MonoidHom from the product type into the additive monoid algebra.

                                                Note the order of the elements of the product are reversed compared to the arguments of Finsupp.single.

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                                                  theorem AddMonoidAlgebra.mul_single_apply_aux {k : Type u₁} {G : Type u₂} [Semiring k] [Add G] (f : AddMonoidAlgebra k G) (r : k) (x : G) (y : G) (z : G) (H : ∀ (a : G), a + x = z a = y) :
                                                  (f * AddMonoidAlgebra.single x r) z = f y * r
                                                  theorem AddMonoidAlgebra.mul_single_zero_apply {k : Type u₁} {G : Type u₂} [Semiring k] [AddZeroClass G] (f : AddMonoidAlgebra k G) (r : k) (x : G) :
                                                  (f * AddMonoidAlgebra.single 0 r) x = f x * r
                                                  theorem AddMonoidAlgebra.mul_single_apply_of_not_exists_add {k : Type u₁} {G : Type u₂} [Semiring k] [Add G] (r : k) {g : G} {g' : G} (x : AddMonoidAlgebra k G) (h : ¬∃ (d : G), g' = d + g) :
                                                  theorem AddMonoidAlgebra.single_mul_apply_aux {k : Type u₁} {G : Type u₂} [Semiring k] [Add G] (f : AddMonoidAlgebra k G) (r : k) (x : G) (y : G) (z : G) (H : ∀ (a : G), x + a = y a = z) :
                                                  (AddMonoidAlgebra.single x r * f) y = r * f z
                                                  theorem AddMonoidAlgebra.single_zero_mul_apply {k : Type u₁} {G : Type u₂} [Semiring k] [AddZeroClass G] (f : AddMonoidAlgebra k G) (r : k) (x : G) :
                                                  (AddMonoidAlgebra.single 0 r * f) x = r * f x
                                                  theorem AddMonoidAlgebra.single_mul_apply_of_not_exists_add {k : Type u₁} {G : Type u₂} [Semiring k] [Add G] (r : k) {g : G} {g' : G} (x : AddMonoidAlgebra k G) (h : ¬∃ (d : G), g' = g + d) :
                                                  theorem AddMonoidAlgebra.mul_single_apply {k : Type u₁} {G : Type u₂} [Semiring k] [AddGroup G] (f : AddMonoidAlgebra k G) (r : k) (x : G) (y : G) :
                                                  (f * AddMonoidAlgebra.single x r) y = f (y - x) * r
                                                  theorem AddMonoidAlgebra.single_mul_apply {k : Type u₁} {G : Type u₂} [Semiring k] [AddGroup G] (r : k) (x : G) (f : AddMonoidAlgebra k G) (y : G) :
                                                  (AddMonoidAlgebra.single x r * f) y = r * f (-x + y)
                                                  theorem AddMonoidAlgebra.liftNC_smul {k : Type u₁} {G : Type u₂} [Semiring k] {R : Type u_3} [AddZeroClass G] [Semiring R] (f : k →+* R) (g : Multiplicative G →* R) (c : k) (φ : MonoidAlgebra k G) :
                                                  (AddMonoidAlgebra.liftNC f g) (c φ) = f c * (AddMonoidAlgebra.liftNC f g) φ
                                                  theorem AddMonoidAlgebra.induction_on {k : Type u₁} {G : Type u₂} [Semiring k] [AddMonoid G] {p : AddMonoidAlgebra k GProp} (f : AddMonoidAlgebra k G) (hM : ∀ (g : G), p ((AddMonoidAlgebra.of k G) (Multiplicative.ofAdd g))) (hadd : ∀ (f g : AddMonoidAlgebra k G), p fp gp (f + g)) (hsmul : ∀ (r : k) (f : AddMonoidAlgebra k G), p fp (r f)) :
                                                  p f
                                                  @[simp]
                                                  theorem AddMonoidAlgebra.mapDomainRingHom_apply {G : Type u₂} (k : Type u_3) [Semiring k] {H : Type u_4} {F : Type u_5} [AddMonoid G] [AddMonoid H] [FunLike F G H] [AddMonoidHomClass F G H] (f : F) :
                                                  def AddMonoidAlgebra.mapDomainRingHom {G : Type u₂} (k : Type u_3) [Semiring k] {H : Type u_4} {F : Type u_5} [AddMonoid G] [AddMonoid H] [FunLike F G H] [AddMonoidHomClass F G H] (f : F) :

                                                  If f : G → H is an additive homomorphism between two additive monoids, then Finsupp.mapDomain f is a ring homomorphism between their add monoid algebras.

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                                                    Conversions between AddMonoidAlgebra and MonoidAlgebra #

                                                    We have not defined k[G] = MonoidAlgebra k (Multiplicative G) because historically this caused problems; since the changes that have made nsmul definitional, this would be possible, but for now we just construct the ring isomorphisms using RingEquiv.refl _.

                                                    The equivalence between AddMonoidAlgebra and MonoidAlgebra in terms of Multiplicative

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                                                      The equivalence between MonoidAlgebra and AddMonoidAlgebra in terms of Additive

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                                                        Non-unital, non-associative algebra structure #

                                                        instance AddMonoidAlgebra.isScalarTower_self (k : Type u₁) {G : Type u₂} {R : Type u_2} [Semiring k] [DistribSMul R k] [Add G] [IsScalarTower R k k] :
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                                                        instance AddMonoidAlgebra.smulCommClass_self (k : Type u₁) {G : Type u₂} {R : Type u_2} [Semiring k] [DistribSMul R k] [Add G] [SMulCommClass R k k] :

                                                        Note that if k is a CommSemiring then we have SMulCommClass k k k and so we can take R = k in the below. In other words, if the coefficients are commutative amongst themselves, they also commute with the algebra multiplication.

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                                                        instance AddMonoidAlgebra.smulCommClass_symm_self (k : Type u₁) {G : Type u₂} {R : Type u_2} [Semiring k] [DistribSMul R k] [Add G] [SMulCommClass k R k] :
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                                                        Algebra structure #

                                                        @[simp]
                                                        theorem AddMonoidAlgebra.singleZeroRingHom_apply {k : Type u₁} {G : Type u₂} [Semiring k] [AddMonoid G] :
                                                        ∀ (a : k), AddMonoidAlgebra.singleZeroRingHom a = (↑(Finsupp.singleAddHom 0)).toFun a

                                                        Finsupp.single 0 as a RingHom

                                                        Equations
                                                        • AddMonoidAlgebra.singleZeroRingHom = { toFun := (↑(Finsupp.singleAddHom 0)).toFun, map_one' := , map_mul' := , map_zero' := , map_add' := }
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                                                          theorem AddMonoidAlgebra.ringHom_ext {k : Type u₁} {G : Type u₂} {R : Type u_3} [Semiring k] [AddMonoid G] [Semiring R] {f : AddMonoidAlgebra k G →+* R} {g : AddMonoidAlgebra k G →+* R} (h₀ : ∀ (b : k), f (AddMonoidAlgebra.single 0 b) = g (AddMonoidAlgebra.single 0 b)) (h_of : ∀ (a : G), f (AddMonoidAlgebra.single a 1) = g (AddMonoidAlgebra.single a 1)) :
                                                          f = g

                                                          If two ring homomorphisms from k[G] are equal on all single a 1 and single 0 b, then they are equal.

                                                          theorem AddMonoidAlgebra.ringHom_ext'_iff {k : Type u₁} {G : Type u₂} {R : Type u_3} [Semiring k] [AddMonoid G] [Semiring R] {f : AddMonoidAlgebra k G →+* R} {g : AddMonoidAlgebra k G →+* R} :
                                                          f = g f.comp AddMonoidAlgebra.singleZeroRingHom = g.comp AddMonoidAlgebra.singleZeroRingHom (↑f).comp (AddMonoidAlgebra.of k G) = (↑g).comp (AddMonoidAlgebra.of k G)
                                                          theorem AddMonoidAlgebra.ringHom_ext' {k : Type u₁} {G : Type u₂} {R : Type u_3} [Semiring k] [AddMonoid G] [Semiring R] {f : AddMonoidAlgebra k G →+* R} {g : AddMonoidAlgebra k G →+* R} (h₁ : f.comp AddMonoidAlgebra.singleZeroRingHom = g.comp AddMonoidAlgebra.singleZeroRingHom) (h_of : (↑f).comp (AddMonoidAlgebra.of k G) = (↑g).comp (AddMonoidAlgebra.of k G)) :
                                                          f = g

                                                          If two ring homomorphisms from k[G] are equal on all single a 1 and single 0 b, then they are equal.

                                                          See note [partially-applied ext lemmas].

                                                          @[simp]
                                                          theorem AddMonoidAlgebra.opRingEquiv_apply {k : Type u₁} {G : Type u₂} [Semiring k] [AddCommMonoid G] :
                                                          ∀ (a : (G →₀ k)ᵐᵒᵖ), AddMonoidAlgebra.opRingEquiv a = Finsupp.mapRange MulOpposite.op (MulOpposite.unop a)
                                                          @[simp]
                                                          theorem AddMonoidAlgebra.opRingEquiv_symm_apply {k : Type u₁} {G : Type u₂} [Semiring k] [AddCommMonoid G] :
                                                          ∀ (a : G →₀ kᵐᵒᵖ), AddMonoidAlgebra.opRingEquiv.symm a = MulOpposite.op (Finsupp.mapRange MulOpposite.unop a)

                                                          The opposite of an R[I] is ring equivalent to the AddMonoidAlgebra Rᵐᵒᵖ I over the opposite ring, taking elements to their opposite.

                                                          Equations
                                                          • AddMonoidAlgebra.opRingEquiv = { toEquiv := (MulOpposite.opAddEquiv.symm.trans (Finsupp.mapRange.addEquiv MulOpposite.opAddEquiv)).toEquiv, map_mul' := , map_add' := }
                                                          Instances For
                                                            theorem AddMonoidAlgebra.opRingEquiv_single {k : Type u₁} {G : Type u₂} [Semiring k] [AddCommMonoid G] (r : k) (x : G) :
                                                            theorem AddMonoidAlgebra.prod_single {k : Type u₁} {G : Type u₂} {ι : Type ui} [CommSemiring k] [AddCommMonoid G] {s : Finset ι} {a : ιG} {b : ιk} :
                                                            is, AddMonoidAlgebra.single (a i) (b i) = AddMonoidAlgebra.single (∑ is, a i) (∏ is, b i)