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Independent finite simplicial arrangement theorem

Statement

For a finite central real hyperplane arrangement with open simplicial chambers, the complexified complement is aspherical. Its fundamental groupoid on chamber basepoints is the groupoid completion of positive galleries modulo equal-endpoint minimal-gallery relations. The positive gallery category has a finite-type atomic categorical Garside structure: the automorphism is antipodes, the Garside arrow at A is u(A,−A), its simple arrows are minimal galleries, and both outgoing left-divisibility and incoming right-divisibility orders are lattices.

Facts & Assumptions

[F1]

Use Positive gallery category, cancellation and length for the finite central arrangement, open simplicial chambers, the positive gallery category P, its minimal-gallery congruence and the classes u(A,B). Use Path presentations, congruences and formal inverses for the groupoid completion of this category. Products follow traversal order.

[F2]

Use Antipodal transformation and finite-type Garside structure for the antipodal Garside structure and Categorical Garside structures and simple arrows for finite type, simple arrows, atomicity and the two divisibility-lattice conditions.

[F3]

Use Complexified complements in an open convex cone with T=V for the complexified complement Y, Fundamental groupoid of a space for endpoint-fixed path-homotopy classes and their composition, and Eilenberg--Mac Lane space for the K(π,1) convention. Choose a real basepoint bA in each chamber A. The groupoid on chamber basepoints means the full subgroupoid with objects bA and all endpoint-fixed path-homotopy classes in Y between them, composed in traversal order.

[F4]

Use Gallery fractions, fundamental groupoid and asphericity for the identification of the gallery completion with this full fundamental subgroupoid and for asphericity, under the same finite central simplicial hypotheses. The substantial arrangement-theoretic inputs are imported in the two supplier lemmas, whose source records give their locators and reading limits; this item composes their conclusions.

Proof

Given: The data and hypotheses in the Statement.

Goal: Establish the Statement.

1.1F1F2given

Apply Antipodal transformation and finite-type Garside structure to the category P of [F1] for the given finite central simplicial arrangement. Its hypotheses are exactly those given. In the convention of [F2], it identifies both divisibility lattices and all of the atomic Garside data stated above, including the antipodal automorphism, the arrow u(A,−A) and minimal gallery classes as the simple arrows.

2.1F1F3F4step 1.1∎

Apply Gallery fractions, fundamental groupoid and asphericity to the same arrangement and the complement Y of [F3]. With the positive wall-crossing convention of that lemma, it identifies the groupoid completion of P with the full fundamental subgroupoid on the chosen chamber basepoints, and gives asphericity of Y. These are the remaining assertions. The finite central simplicial hypotheses must be checked afresh for any restricted arrangement consuming this theorem. No infinite or nonsimplicial arrangement is covered.

Depends on

Used by · 3

Dependency tree · 2 levels

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