Dedekind domains #
This file defines the notion of a Dedekind domain (or Dedekind ring), giving three equivalent definitions (TODO: and shows that they are equivalent).
Main definitions #
is_dedekind_domain
defines a Dedekind domain as a commutative ring that is not a field, Noetherian, integrally closed in its field of fractions and has Krull dimension exactly one.is_dedekind_domain_iff
shows that this does not depend on the choice of field of fractions.is_dedekind_domain_dvr
alternatively defines a Dedekind domain as an integral domain that is not a field, Noetherian, and the localization at every nonzero prime ideal is a DVR.is_dedekind_domain_inv
alternatively defines a Dedekind domain as an integral domain that is not a field, and every nonzero fractional ideal is invertible.is_dedekind_domain_inv_iff
shows that this does note depend on the choice of field of fractions.
Implementation notes #
The definitions that involve a field of fractions choose a canonical field of fractions,
but are independent of that choice. The ..._iff
lemmas express this independence.
References #
Tags #
dedekind domain, dedekind ring
A ring R
has Krull dimension at most one if all nonzero prime ideals are maximal.
Equations
- ring.dimension_le_one R = ∀ (p : ideal R), p ≠ ⊥ → p.is_prime → p.is_maximal
- not_is_field : ¬is_field A
- is_noetherian_ring : is_noetherian_ring A
- dimension_le_one : ring.dimension_le_one A
- is_integrally_closed : integral_closure A (fraction_ring A) = ⊥
A Dedekind domain is an integral domain that is Noetherian, integrally closed, and
has Krull dimension exactly one (not_is_field
and dimension_le_one
).
The integral closure condition is independent of the choice of field of fractions:
use is_dedekind_domain_iff
to prove is_dedekind_domain
for a given fraction_map
.
This is the default implementation, but there are equivalent definitions,
is_dedekind_domain_dvr
and is_dedekind_domain_inv
.
TODO: Prove that these are actually equivalent definitions.
An integral domain is a Dedekind domain iff and only if it is not a field, is Noetherian, has dimension ≤ 1, and is integrally closed in a given fraction field. In particular, this definition does not depend on the choice of this fraction field.
- not_is_field : ¬is_field A
- is_noetherian_ring : is_noetherian_ring A
- is_dvr_at_nonzero_prime : ∀ (P : ideal A), P ≠ ⊥ → ∀ (ᾰ : P.is_prime), discrete_valuation_ring (localization.at_prime P)
A Dedekind domain is an integral domain that is not a field, is Noetherian, and the localization at every nonzero prime is a discrete valuation ring.
This is equivalent to is_dedekind_domain
.
TODO: prove the equivalence.
Equations
- ring.fractional_ideal.has_inv K = {inv := λ (I : ring.fractional_ideal g), 1 / I}
I⁻¹
is the inverse of I
if I
has an inverse.
- not_is_field : ¬is_field A
- mul_inv_cancel : ∀ (I : ring.fractional_ideal (fraction_ring.of A)), I ≠ ⊥ → I * (1 / I) = 1
A Dedekind domain is an integral domain that is not a field such that every fractional ideal has an inverse.
This is equivalent to is_dedekind_domain
.
TODO: prove the equivalence.