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We study outer Lipschitz geometry of real semialgebraic or, more general, definable in a polynomially bounded o-minimal structure over the reals, surface germs. In particular, any definable H\"older triangle is either Lipschitz normally…

Metric Geometry · Mathematics 2021-08-30 Andrei Gabrielov , Emanoel Souza

The abnormal surfaces called snakes and circular snakes, defined in \cite{GabrielovSouza}, are special types of surface germs capturing the outer Lipschitz phenomena relevant to the outer classification problem. We provide algorithms to…

Metric Geometry · Mathematics 2025-06-02 Davi Lopes Medeiros , Euripedes Carvalho da Silva , Emanoel Souza

We present here basic results in Lipschitz Geometry of semialgebraic surface germs. Although bi-Lipschitz classification problem of surface germs with respect to the inner metric was solved long ago, classification with respect to the outer…

Metric Geometry · Mathematics 2022-12-13 Lev Birbrair , Andrei Gabrielov

We study the ambient Lipschitz geometry of semialgebraic surfaces. It was discovered in \cite{BBG} that ambient Lipschitz Geometry is different from the outer Lipschtz geometry. We show that two surface germs in $\mathbb{R}^3$, Lipschitz…

Metric Geometry · Mathematics 2024-12-02 Lev Birbrair , Davi Lopes Medeiros

We consider a special case of the outer bi-Lipschitz classification of real semialgebraic (or, more general, definable in a polynomially bounded o-minimal structure) surface germs, obtained as a union of two normally embedded H\"older…

Metric Geometry · Mathematics 2022-07-21 Lev Birbrair , Andrei Gabrielov

We undertake a systematic study of Lipschitz Normally Embedded normal complex surface germs. We prove in particular that the topological type of such a germ determines the combinatorics of its minimal resolution which factors through the…

Algebraic Geometry · Mathematics 2022-06-01 André Belotto da Silva , Lorenzo Fantini , Anne Pichon

The aim of this paper to introduce the reader to a recent point of view on the Lipschitz classifications of complex singularities. It presents the complete classification of Lipschitz geometry of complex plane curves singularities and in…

Algebraic Geometry · Mathematics 2020-07-09 Anne Pichon

We introduce several commutative rings, the snake rings, that have strong connections to cluster algebras. The elements of these rings are residue classes of unions of certain labeled graphs that were used to construct canonical bases in…

Combinatorics · Mathematics 2015-07-07 Ilke Canakci , Ralf Schiffler

A link at the origin of an isolated singularity of a two-dimensional semialgebraic surface in $\mathbb{R}^4$ is a topological knot (or link) in $S^3$. We study the connection between the ambient Lipschitz geometry of semialgebraic surface…

Algebraic Geometry · Mathematics 2022-03-22 Lev Birbrair , Michael Brandenbursky , Andrei Gabrielov

We prove that the outer Lipschitz geometry of a germ $(X,0)$ of a normal complex surface singularity determines a large amount of its analytic structure. In particular, it follows that any analytic family of normal surface singularities…

Algebraic Geometry · Mathematics 2016-02-18 Walter D. Neumann , Anne Pichon

We investigate the relationships between the Lipschitz outer geometry and the embedded topological type of a hypersurface germ in $(\mathbb C^n,0)$. It is well known that the Lipschitz outer geometry of a complex plane curve germ determines…

Algebraic Geometry · Mathematics 2015-11-26 Walter D. Neumann , Anne Pichon

In this paper, we prove that two normal complex surface germs that are inner bilipschitz--but not necessarily orientation-preserving--homeomorphic, have in fact the same oriented topological type and the same minimal plumbing graph. Along…

Algebraic Geometry · Mathematics 2025-11-10 Lorenzo Fantini , Anne Pichon

Snake graphs appear naturally in the theory of cluster algebras. For cluster algebras from surfaces, each cluster variable is given by a formula which is parametrized by the perfect matchings of a snake graph. In this paper, we continue our…

Representation Theory · Mathematics 2014-07-30 Ilke Canakci , Ralf Schiffler

Any subanalytic germ $(X,0) \subset (\mathbb R^n,0)$ is equipped with two natural metrics: its outer metric, induced by the standard Euclidean metric of the ambient space, and its inner metric, which is defined by measuring the shortest…

Algebraic Geometry · Mathematics 2025-01-07 Lorenzo Fantini , Anne Pichon

A link of an isolated singularity of a two-dimensional semialgebraic surface in $R^4$ is a knot (or a link) in $S^3$. Thus the ambient Lipschitz classification of surface singularities in $R^4$ can be interpreted as a bi-Lipschitz…

Algebraic Geometry · Mathematics 2020-02-14 Lev Birbrair , Andrei Gabrielov

Geodesic tracking on the projective line bundle $\R^2 \times P^1 $ has many uses, including the segmentation of objects in images. However, global tracking requires expensive distance map computations. We provide a practical solution to…

Differential Geometry · Mathematics 2026-04-14 Leanne Vis , Maxim Pisarenco , Bart M. N. Smets , Fons van der Sommen , Remco Duits

We give an explicit combinatorial formula for the Laurent expansion of any arc or closed curve on an unpunctured triangulated orbifold. We do this by extending the snake graph construction of Musiker, Schiffler, and Williams to unpunctured…

Combinatorics · Mathematics 2020-12-18 Esther Banaian , Elizabeth Kelley

A normal pair of H\"older triangles is the union of two normally embedded H\"older triangles satisfying some natural conditions on the tangency orders of their boundary arcs. It is a special case of a surface germ, a germ at the origin of a…

Metric Geometry · Mathematics 2024-12-19 Lev Birbrair , Andrei Gabrielov

The aim of the article is to understand the combinatorics of snake graphs by means of linear algebra. In particular, we apply Kasteleyn's and Temperley--Fisher's ideas about spectral properties of weighted adjacency matrices of planar…

Combinatorics · Mathematics 2019-10-28 James P. Bradshaw , Philipp Lampe , Dusan Ziga

We describe the Lipschitz geometry of complex curves. For the most part this is well known material, but we give a stronger version even of known results. In particular, we give a quick proof, without any analytic restrictions, that the…

Algebraic Geometry · Mathematics 2015-03-17 Walter D. Neumann , Anne Pichon
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