The regulator is independent of the generators and of the deleted column, and positive
ProvedDirichletUnitTheorem.regulator_well_definedLet be a number field, , and let and be two systems of generators of modulo roots of unity. Form the matrices and , columns indexed by the infinite places. Delete any one column from the first and any one column from the second. Then the two square submatrices have determinants of the same absolute value , and .
This common value is the regulator of ; the statement says it does not depend on the choice of generators nor on the deleted column, and is a positive real number.
Formalization Note Deleting the column of place leaves a square matrix whose rows and columns are both indexed by the places , the rows being matched to through an arbitrary bijection ; reordering rows only changes the sign of the determinant.
import Mathlib open NumberField
namespace DirichletUnitTheorem
theorem regulator_well_defined (K : Type*) [Field K] [NumberField K]
[DecidableEq (InfinitePlace K)]
(u v : Fin (InfinitePlace.nrRealPlaces K + InfinitePlace.nrComplexPlaces K - 1) → (𝓞 K)ˣ)
(hu : ∀ x : (𝓞 K)ˣ, ∃ ζ : (𝓞 K)ˣ, IsOfFinOrder ζ ∧ ∃ n : Fin _ → ℤ, x = ζ * ∏ i, u i ^ n i)
(hv : ∀ x : (𝓞 K)ˣ, ∃ ζ : (𝓞 K)ˣ, IsOfFinOrder ζ ∧ ∃ n : Fin _ → ℤ, x = ζ * ∏ i, v i ^ n i)
(w₁ w₂ : InfinitePlace K)
(e₁ : {w // w ≠ w₁} ≃ Fin (InfinitePlace.nrRealPlaces K + InfinitePlace.nrComplexPlaces K - 1))
(e₂ : {w // w ≠ w₂} ≃ Fin (InfinitePlace.nrRealPlaces K + InfinitePlace.nrComplexPlaces K - 1)) :
|(Matrix.of fun (i j : {w // w ≠ w₁}) =>
((j : InfinitePlace K).mult : ℝ) * Real.log ((j : InfinitePlace K) ((u (e₁ i) : 𝓞 K) : K))).det| =
|(Matrix.of fun (i j : {w // w ≠ w₂}) =>
((j : InfinitePlace K).mult : ℝ) * Real.log ((j : InfinitePlace K) ((v (e₂ i) : 𝓞 K) : K))).det| ∧
0 < |(Matrix.of fun (i j : {w // w ≠ w₁}) =>
((j : InfinitePlace K).mult : ℝ) * Real.log ((j : InfinitePlace K) ((u (e₁ i) : 𝓞 K) : K))).det| := by sorry
end DirichletUnitTheoremRead-back
What the Lean code literally says, in plain math · Aristotle (Harmonic) — same agent as the drafter; non-blind
Non-blind read-back — not independent testimony. This read-back was written by the same agent (Aristotle, by Harmonic) that drafted this Lean statement, at the explicit request of the account owner. Its author knew the intended meaning while writing it, so it must not be mistaken for a blind audit by an independent reviewer. Please compare it against the Lean code itself.
Throughout, is a number field (a field of characteristic zero that is finite-dimensional over ), is its ring of integers and the unit group. denotes the number of real infinite places of and the number of complex infinite places (each complex place corresponds to a pair of complex-conjugate embeddings ). For an infinite place of , denotes the absolute value for an embedding inducing , and is if is real and if is complex. is the real logarithm (Mathlib's convention gives , but units have ). Let (truncated subtraction). Statement. Let be a number field (with a chosen decidable equality on its infinite places, needed to form determinants; the value does not depend on it). Let be families of units such that every unit can be written as for some unit of finite order and some integers , and likewise for (only existence of such a representation is assumed, not uniqueness). Let be infinite places, and let (resp. ) be any bijection from the set of infinite places different from (resp. ) onto . Define the square matrix with rows and columns indexed by the places by , and analogously with . Then
Confirmed by the mission captain (proposal self-audit).
Confirmed by the moderator at approval.