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Let X be a projective complex 3-fold, quasihomogeneous with respect to an action of a linear algebraic group. We show that X is a compactification of SL_2/G, G a discrete subgroup, or that X can be equivariantly transformed into the 3-dim.…

Algebraic Geometry · Mathematics 2007-05-23 Stefan Kebekus

How complex must two finite 2-complexes be to admit a common, but not finite common, covering? We obtain an almost answer: the minimum possible number of triangles in a pseudo-simplicial triangulation of each complex is 3, 4, or 5.

Geometric Topology · Mathematics 2025-05-06 Natalia S. Dergacheva , Anton A. Klyachko

We prove that a planar graph is generically rigid in the plane if and only if it can be embedded as a pseudo-triangulation. This generalizes the main result of math.CO/0307347 which treats the minimally generically rigid case. The proof…

Combinatorics · Mathematics 2007-05-24 David Orden , Francisco Santos , Brigitte Servatius , Herman Servatius

Through computer enumeration with the aid of topological results, we catalogue all 18 closed non-orientable P^2-irreducible 3-manifolds that can be formed from at most eight tetrahedra. In addition we give an overview as to how the 100…

Geometric Topology · Mathematics 2010-12-21 Benjamin A. Burton

We develop a novel technique, which we call poset splitting, that allows us to solve two open problems regarding minimality of finite models of spaces: the nonexistence of a finite model of the real projective plane with fewer than 13…

Algebraic Topology · Mathematics 2015-12-21 Nicolás Cianci , Miguel Ottina

Multi-view Geometry is reviewed from an Algebraic Geometry perspective and multi-focal tensors are constructed as equivariant projections of the Grassmannian. A connection to the principal minor assignment problem is made by considering…

Algebraic Geometry · Mathematics 2025-10-17 Luke Oeding

In the present note we focus on conic line arrangements in the plane with quasihomogeneous ordinary singularities from the perspective of weak Ziegler pairs. The foundations of this article come from an active area of research devoted to…

Algebraic Geometry · Mathematics 2024-03-26 Magdalena Lampa-Baczyńska , Daniel Wojcik

Motivated by the analogies between the projective and the almost quaternionic geometries, we study the generalized planar curves and mappings. We follow, recover, and extend the classical approach as developed by Mikes and Sinyukov. Then we…

Differential Geometry · Mathematics 2007-05-23 Jaroslav Hrdina , Jan Slovak

I consider the class of surfaces $X$ over algebraically closed fields with numerical invariants given in the title. In characteristic zero, this class contains fake projective planes which were introduced by David Mumford. I prove that in…

Algebraic Geometry · Mathematics 2025-08-19 Kirti Joshi

We construct an infinite family of 4-polytopes whose realization spaces have dimension smaller or equal to 96. This in particular settles a problem going back to Legendre and Steinitz: whether and how the dimension of the realization space…

Combinatorics · Mathematics 2014-03-20 Karim A. Adiprasito , Günter M. Ziegler

The addendum updates the results presented in the paper `Fake Projective Plane, Invent Math 168, 321-370 (2007)' and makes some additions and corrections. The fake projective planes are classified into twenty six classes. Together with a…

Algebraic Geometry · Mathematics 2015-05-13 Gopal Prasad , Sai-Kee Yeung

Compact pseudo-Riemannian manifolds that have parallel Weyl tensor without being conformally flat or locally symmetric are known to exist in infinitely many dimensions greater than 4. We prove some general topological properties of such…

Differential Geometry · Mathematics 2011-06-07 Andrzej Derdzinski , Witold Roter

Coxeter pointed out that a number of polytopes can be projected orthogonally into two dimensions in such a way that their vertices lie on a number of concentric regular triacontagons (or 30-gons). Among them are the 600-cell and 120-cell in…

Combinatorics · Mathematics 2026-04-16 P. K. Aravind , Justin Y. J. Burton , Guillermo Núñez Ponasso , D. Richter

The estimate for the maximal number of ordinary double points of a projective surface of degree eight is improved to $168\leq\mu(8)\leq 174$ by constructing a projective surface of degree eight with 168 nodes.

alg-geom · Mathematics 2008-02-03 Stephan Endrass

We present a simplified proof of a forty-year-old result concerning the tiling of the plane with equilateral convex polygons. Our approach is based on a theorem by M. Rao, who used an exhaustive computer search to confirm the completeness…

Metric Geometry · Mathematics 2025-11-11 Bernhard Klaassen

This report gives an overview of the history of finite projective planes and their properties before going on to outline the proof that no projective plane of order 10 exists. The report also investigates the search carried out by…

History and Overview · Mathematics 2016-03-18 Xander Perrott

In the 1980s, Neumann and Zagier introduced a symplectic vector space associated to an ideal triangulation of a cusped 3-manifold, such as a knot complement. We give a geometric interpretation for this symplectic structure in terms of the…

Geometric Topology · Mathematics 2025-09-01 Daniel V. Mathews , Jessica S. Purcell

The action of the mapping class group of the thrice-punctured projective plane on its $\mathrm{GL}(2,\mathbb{C})$ character variety produces an algorithm for generating the simple length spectra of quasi-Fuchsian thrice-punctured projective…

Geometric Topology · Mathematics 2014-11-19 Yi Huang , Paul Norbury

We prove that 1) There exist infinitely many non-trivial codimension one "thick" knots in $\mathbb{R}^5$; 2) For each closed four-dimensional smooth manifold $M$ and for each sufficiently small positive $\epsilon$ the set of isometry…

Metric Geometry · Mathematics 2016-03-17 Boris Lishak , Alexander Nabutovsky

Transversal structures (also known as regular edge labelings) are combinatorial structures defined over 4-connected plane triangulations with quadrangular outer-face. They have been intensively studied and used for many applications…

Discrete Mathematics · Computer Science 2017-07-27 Nicolas Bonichon , Benjamin Lévêque