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Currying of an irreducible positive-degree plane polynomial is primitive

Proved
PachDeZeeuw.Algebraic.curry_isPrimitive_of_irreducible_positive_natDegree

by mysticflounder · Sep 17, 2026 · Mathlib 0df444a (Lean v4.33.1)

pach-de-zeeuw-bezoutplane-curvesprimitivityresultants

Let hhh be an irreducible bivariate real polynomial (Irreducible h\mathrm{Irreducible}\,hIrreducibleh) whose currying has positive degree, 0<(Curry0(h)).natDegree0 < (\mathrm{Curry}_0(h)).\mathrm{natDegree}0<(Curry0​(h)).natDegree. Then the curried univariate polynomial over the coefficient ring is primitive:

IsPrimitive(Curry0(h)).\mathrm{IsPrimitive}(\mathrm{Curry}_0(h)).IsPrimitive(Curry0​(h)).

Primitivity (content a unit) is the hypothesis needed for Gauss-type arguments: it allows coprimality over the coefficient ring to be transported to the fraction field, where the resultant nonvanishing argument runs.

Preamble
import Mathlib
import Definitions.Def_PdzPrelim

open EuclideanGeometry
open scoped Topology
open PachDeZeeuw.Algebraic
open PachDeZeeuw.Algebraic.PlaneCurve
Formal statement
theorem PachDeZeeuw.Algebraic.curry_isPrimitive_of_irreducible_positive_natDegree (h : MvPolynomial (Fin 2) ℝ)
    (hh : Irreducible h)
    (hpos : 0 < (Curry0 h).natDegree) :
    (Curry0 h).IsPrimitive := by sorry
Source
Standard algebra used in proving Bézout's inequality, Theorem 2.1 of Pach–de Zeeuw, Distinct distances on algebraic curves in the plane (arXiv:1308.0177), which cites Gibson, Elementary Geometry of Algebraic Curves, Lemma 14.4; this lemma is not stated in the paper; formalized in https://github.com/mysticflounder/lean-formalizations/blob/dd46c17a2a034d7bfa0df02e7f77834d35592864/lean/LeanFormalizations/PachDeZeeuw/AlgebraicPrelim.lean#L1086-L1096
Human review
  • Endorsed by Shuze Chen · Sep 17, 2026

  • Endorsed by mysticflounder · Sep 17, 2026

    Confirmed by the mission captain (proposal self-audit).

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