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Mathlib.Algebra.Ring.Basic

Semirings and rings #

This file gives lemmas about semirings, rings and domains. This is analogous to Algebra.Group.Basic, the difference being that the former is about + and * separately, while the present file is about their interaction.

For the definitions of semirings and rings see Algebra.Ring.Defs.

def AddHom.mulLeft {R : Type u_1} [Distrib R] (r : R) :

Left multiplication by an element of a type with distributive multiplication is an AddHom.

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    @[simp]
    theorem AddHom.mulLeft_apply {R : Type u_1} [Distrib R] (r : R) :
    (AddHom.mulLeft r) = fun (x : R) => r * x
    def AddHom.mulRight {R : Type u_1} [Distrib R] (r : R) :

    Left multiplication by an element of a type with distributive multiplication is an AddHom.

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      @[simp]
      theorem AddHom.mulRight_apply {R : Type u_1} [Distrib R] (r : R) :
      (AddHom.mulRight r) = fun (a : R) => a * r

      Left multiplication by an element of a (semi)ring is an AddMonoidHom

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        Right multiplication by an element of a (semi)ring is an AddMonoidHom

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          @[simp]
          theorem AddMonoidHom.coe_mulRight {R : Type u_1} [NonUnitalNonAssocSemiring R] (r : R) :
          (AddMonoidHom.mulRight r) = fun (x : R) => x * r
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          @[simp]
          theorem inv_neg' {α : Type u_2} [Group α] [HasDistribNeg α] (a : α) :
          theorem vieta_formula_quadratic {α : Type u_2} [NonUnitalCommRing α] {b c x : α} (h : x * x - b * x + c = 0) :
          ∃ (y : α), y * y - b * y + c = 0 x + y = b x * y = c

          Vieta's formula for a quadratic equation, relating the coefficients of the polynomial with its roots. This particular version states that if we have a root x of a monic quadratic polynomial, then there is another root y such that x + y is negative the a_1 coefficient and x * y is the a_0 coefficient.

          theorem succ_ne_self {α : Type u_2} [NonAssocRing α] [Nontrivial α] (a : α) :
          a + 1 a
          theorem pred_ne_self {α : Type u_2} [NonAssocRing α] [Nontrivial α] (a : α) :
          a - 1 a
          @[instance 100]