Units of a number field #
We prove some basic results on the group (π K)Λ£
of units of the ring of integers π K
of a number
field K
and its torsion subgroup.
Main definition #
NumberField.Units.torsion
: the torsion subgroup of a number field.
Main results #
NumberField.isUnit_iff_norm
: an algebraic integerx : π K
is a unit if and only if|norm β x| = 1
.NumberField.Units.mem_torsion
: a unitx : (π K)Λ£
is torsion iffw x = 1
for all infinite placesw
ofK
.
Tags #
number field, units
Equations
- NumberField.Units.instCoeHTCUnitsRingOfIntegers K = { coe := fun (x : (NumberField.RingOfIntegers K)Λ£) => (algebraMap (NumberField.RingOfIntegers K) K) βx }
The group homomorphism (π K)Λ£ β* βΛ£
induced by a complex embedding of K
.
Equations
- NumberField.Units.complexEmbedding Ο = (Units.map βΟ).comp (Units.map β(algebraMap (NumberField.RingOfIntegers K) K))
Instances For
The torsion subgroup of the group of units.
Equations
Instances For
The torsion subgroup is finite.
The torsion subgroup is cyclic.
The order of the torsion subgroup.
Equations
Instances For
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
.