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Conjugacy of the odd-order elements is read off from the permutation layer (Theorem 5)

Disproved
BQC.conjugacy_cycle_type

by Lucas · Oct 22, 2026 · Mathlib 0df444a (Lean v4.33.1)

braid-groupsconjugacy

Two elements of the braid quotient of the same odd order k at least three are conjugate in the quotient if and only if their images are conjugate in the permutation layer. Conjugacy of the finite-order elements of odd order at least three is thus determined by the cycle types of the permutations; likewise two cyclic subgroups of the same odd order are conjugate exactly when their images are conjugate in the permutation layer. This is Theorem 5 of the source paper, the main result of its Section 6.

Preamble
import Mathlib
import Definitions.Def_BQC_alg
import Definitions.Def_BQC_tor
Formal statement
namespace BQC

/-!  Milestone 5 (Theorem 5): two elements of the braid quotient of the same
odd order at least three are conjugate in the quotient if and only if their
images are conjugate in the permutation layer. Conjugacy of elements of odd
order is read off from the permutation layer; likewise two cyclic subgroups of
the same odd order are conjugate exactly when their images are. -/
theorem conjugacy_cycle_type {n : Nat} {Q S : Type*} [Group Q] [Group S] [Fintype S]
    (W : BraidQuotient n Q S) (k : Nat) (hk : 3 ≤ k) (hodd : Odd k)
    (x y : Q) (hx : ExactOrder k x) (hy : ExactOrder k y) :
    (∃ c : Q, c * x * c⁻¹ = y) ↔
      (∃ s : S, s * W.proj x * s⁻¹ = W.proj y) := by sorry

end BQC
Source
D. L. Goncalves, J. Guaschi, O. Ocampo, A quotient of the Artin braid groups related to crystallographic groups, Journal of Algebra 474 (2017) 393-423, Section 6 (Theorem 5).
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What the Lean code literally says, in plain math · glm-5-latest-short

Restate: for the braid quotient world, two elements of exact order k - with k at least three and odd - are conjugate in the quotient if and only if there is an element of the permutation layer conjugating the projection of the one to the projection of the other. Hypotheses: k is at least three and odd; both elements have exact order k.

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