Documentation

Mathlib.NumberTheory.NumberField.Units.Basic

Units of a number field #

We prove some basic results on the group (π“ž K)Λ£ of units of the ring of integers π“ž K of a number field K and its torsion subgroup.

Main definition #

Main results #

Tags #

number field, units

theorem NumberField.Units.coe_coe {K : Type u_1} [Field K] (u : (RingOfIntegers K)Λ£) :
↑↑u = (algebraMap (RingOfIntegers K) K) ↑u
theorem NumberField.Units.coe_mul {K : Type u_1} [Field K] (x y : (RingOfIntegers K)Λ£) :
(algebraMap (RingOfIntegers K) K) ↑(x * y) = (algebraMap (RingOfIntegers K) K) ↑x * (algebraMap (RingOfIntegers K) K) ↑y
theorem NumberField.Units.coe_pow {K : Type u_1} [Field K] (x : (RingOfIntegers K)Λ£) (n : β„•) :
(algebraMap (RingOfIntegers K) K) ↑(x ^ n) = (algebraMap (RingOfIntegers K) K) ↑x ^ n
theorem NumberField.Units.coe_zpow {K : Type u_1} [Field K] (x : (RingOfIntegers K)Λ£) (n : β„€) :
(algebraMap (RingOfIntegers K) K) ↑(x ^ n) = (algebraMap (RingOfIntegers K) K) ↑x ^ n
theorem NumberField.Units.coe_one {K : Type u_1} [Field K] :
(algebraMap (RingOfIntegers K) K) ↑1 = 1
theorem NumberField.Units.coe_neg_one {K : Type u_1} [Field K] :
(algebraMap (RingOfIntegers K) K) ↑(-1) = -1

The group homomorphism (π“ž K)Λ£ β†’* β„‚Λ£ induced by a complex embedding of K.

Equations
Instances For
    @[simp]
    theorem NumberField.Units.complexEmbedding_apply {K : Type u_1} [Field K] (Ο† : K β†’+* β„‚) (u : (RingOfIntegers K)Λ£) :
    ↑((Units.complexEmbedding Ο†) u) = Ο† ((algebraMap (RingOfIntegers K) K) ↑u)
    @[simp]
    theorem NumberField.Units.pos_at_place {K : Type u_1} [Field K] (x : (RingOfIntegers K)Λ£) (w : InfinitePlace K) :
    0 < w ((algebraMap (RingOfIntegers K) K) ↑x)
    theorem NumberField.Units.sum_mult_mul_log {K : Type u_1} [Field K] [NumberField K] (x : (RingOfIntegers K)Λ£) :
    βˆ‘ w : InfinitePlace K, ↑w.mult * Real.log (w ((algebraMap (RingOfIntegers K) K) ↑x)) = 0

    The torsion subgroup of the group of units.

    Equations
    Instances For
      theorem NumberField.Units.mem_torsion (K : Type u_1) [Field K] [NumberField K] {x : (RingOfIntegers K)Λ£} :
      x ∈ torsion K ↔ βˆ€ (w : InfinitePlace K), w ((algebraMap (RingOfIntegers K) K) ↑x) = 1

      The order of the torsion subgroup.

      Equations
      Instances For
        theorem NumberField.Units.rootsOfUnity_eq_one (K : Type u_1) [Field K] [NumberField K] {k : β„•+} (hc : (↑k).Coprime (torsionOrder K)) {ΞΆ : (RingOfIntegers K)Λ£} :
        ΞΆ ∈ rootsOfUnity (↑k) (RingOfIntegers K) ↔ ΞΆ = 1

        If k does not divide torsionOrder then there are no nontrivial roots of unity of order dividing k.

        The group of roots of unity of order dividing torsionOrder is equal to the torsion group.

        The image of torsion K by a complex embedding is the group of complex roots of unity of order torsionOrder K.

        theorem NumberField.Units.torsion_eq_one_or_neg_one_of_odd_finrank {K : Type u_1} [Field K] [NumberField K] (h : Odd (Module.finrank β„š K)) (x : β†₯(torsion K)) :
        ↑x = 1 ∨ ↑x = -1