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PolynomialCurvePlace order support is finite given HasPrincipalDivisors

Proved
OAI.PiExponent.FormalInterpolation.polynomialCurveOrder_support_finite_of_hasPrincipalDivisors

by Ethan Cheung Wang · Oct 21, 2026 · Mathlib 0df444a (Lean v4.33.1)

function-fieldspi-exponentplaces

Assume E/CE/\mathbb{C}E/C admits principal divisors in the sense of AlgebraicCurve.HasPrincipalDivisors: for every nonzero f∈Ef\in Ef∈E the function v↦v.ord(f)v\mapsto v.\mathrm{ord}(f)v↦v.ord(f) on AlgebraicCurve.Place places is the evaluation of a finitely supported divisor.

Then, among the normalized discrete places of type PolynomialCurvePlace (integer-valued additive valuations trivial on C×\mathbb{C}^\timesC× and surjective onto Z\mathbb{Z}Z), only finitely many ν\nuν satisfy ordν(f)≠0\mathrm{ord}_\nu(f)\neq 0ordν​(f)=0.

This is the comparison between the FormalInterpolation place type and the AlgebraicCurve place type: once principal divisors exist for the latter, the nonzero-order locus for the former is finite. The zero function is assigned order zero at every place by the untop₀ convention, so its support is empty.

Preamble
import Definitions.Def_OAI_PiExponent_WeightedIdealCurveCriterion
import Definitions.Def_AlgebraicCurve_DivisorClassGroup

open OAI.PiExponent.FormalInterpolation
open AlgebraicCurve
Formal statement
theorem OAI.PiExponent.FormalInterpolation.polynomialCurveOrder_support_finite_of_hasPrincipalDivisors
    {E : Type} [Field E] [Algebra Complex E]
    [HasPrincipalDivisors Complex E] (f : E) :
    Set.Finite {nu : PolynomialCurvePlace E | polynomialCurveOrder nu f ≠ 0} := by sorry
Source
Bridge lemma for OAI.PiExponent.FormalInterpolation.polynomialCurveOrder_support_finite; compares PolynomialCurvePlace to AlgebraicCurve.Place under HasPrincipalDivisors (cf. AlgebraicCurve.finite_setOf_ord_ne_zero_of_finiteDimensional)

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