The presentation of the link-homotopy classes over a punctured surface (Corollary 3.10)
DisprovedHGL.presentation_puncturedOver the punctured surface, the class group admits the presentation with the generators a and sigma and the relations LH, R1, R2, R4, R5, and R6 - the relations of the closed-surface presentation with the surface relation R3 omitted, since the deleted point removes the relation involving the boundary word. The universal property: any group with a family of sigma elements and a family of a elements satisfying these relations receives a unique homomorphism from the class group mapping the standard generators to the families.
import Mathlib import Definitions.Def_HGL_alg import Definitions.Def_HGL_tor
namespace HGL
/-! Milestone 7 (Corollary 3.10): the link-homotopy class group of a
punctured surface admits the presentation with the generators a_(1,r) and
sigma_i and the relations LH, R1, R2, R4, R5, R6 - the relations of
Theorem 3.9 with the surface relation R3 omitted, since the deleted point
removes the relation involving the boundary word. The universal property:
any group with families satisfying these relations receives a unique
homomorphism from the class group mapping the standard generators to the
families. -/
theorem presentation_punctured {n g : ℕ} {B S Cl : Type*} [Group B] [Monoid S] [Group Cl]
(W : LinkHomotopyWorld n g B S Cl) :
∀ (G : Type) [Group G] (sigma : Fin (n - 1) → G) (a : Fin (2 * g) → G),
SatisfiesPuncturedPresentation W.hn sigma a →
∃! f : Cl →* G, (∀ i : Fin (n - 1), f (W.gen_sigma i) = sigma i) ∧
(∀ r : Fin (2 * g), f (W.gen_a r) = a r) := by sorry
end HGL
Read-back
What the Lean code literally says, in plain math · glm-5-latest-short
Restate: in a link-homotopy world, for any group with a family of n-1 elements and a family of 2g elements satisfying the punctured presentation predicate - the link-homotopy relation LH and the braid relations R1, R2, R4, R5, R6 with the surface relation R3 omitted - there exists exactly one homomorphism from the class group to that group mapping the sigma generators to the first family and the a generators to the second. Hypotheses: the world is given; the target families satisfy the punctured relations; no further hypotheses appear.