Mazur 13 port: principal_between_balanced_of_constant

Proved

MazurProof.N13Mumford.principal_between_balanced_of_constant

by xuanji · Oct 9, 2026 · Mathlib 0df444a (Lean v4.33.1)

huang-flt-portmazur-full-torsionmazur-n13-portorder13

Supporting lemma principal_between_balanced_of_constant (namespace MazurProof.N13Mumford).

This lemma is one step of a machine-checked proof that the genus-two curve

Y^2 = X^6+4X^5+6X^4+2X^3+X^2+2X+1

(a model of $X_1(13)$ ) has no rational affine points other than the cusps $X\in\{0,-1\}$ , which gives the case $N=13$ of Mazur's torsion theorem. The proof is Xiang Huang's Lean development, ported to this Mathlib and split into one node per large lemma; definitions live in the layered entries MazurN13_L0, MazurN13_L1, ….

Preamble

import Mathlib
import Definitions.Def_MazurN13_L2

set_option backward.isDefEq.respectTransparency false
set_option backward.isDefEq.respectTransparency.types false
open MazurProof MazurProof.N13Mumford
open scoped nonZeroDivisors
open SexticMumford
universe u
variable (K : Type u) [Field K] [CharZero K]

Formal statement

theorem MazurProof.N13Mumford.principal_between_balanced_of_constant {D₁ D₂ : Mumford K} {α : (FunctionField K)ˣ} (c : Kˣ) (hα : α = N13Infinity.functionConstUnit K c) (hIdeal : mumfordIdealUnit (model K) D₁.toSemi * toPrincipalIdeal (CoordinateRing K) (FunctionField K) α = mumfordIdealUnit (model K) D₂.toSemi) (hInf : Multiplicative.ofAdd ((D₁.nInf : ℤ) - 1) * (N13Infinity.positiveInfinityOrder K).ordPlus α = Multiplicative.ofAdd ((D₂.nInf : ℤ) - 1)) : D₁ = D₂ := by sorry

Source

Xiang Huang, FLT fork, https://github.com/xiangyazi24/FLT/blob/51bbb4f/FLT/Assumptions/MazurProof/N13MumfordRigidity.lean#L34

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