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Non-trivial examples of generalized paracomplex structures (in the sense of the generalized geometry \`a la Hitchin) are constructed applying the twistor space construction scheme.

Differential Geometry · Mathematics 2024-09-10 Johann Davidov

We construct two combinatorially equivalent line arrangements in the complex projective plane such that the fundamental groups of their complements are not isomorphic. The proof uses a new invariant of the fundamental group of the…

Algebraic Geometry · Mathematics 2015-07-08 Grigory Rybnikov

We investigate the isomorphism types of combinatorial geometries arising from Hrushovski's flat strongly minimal structures and answer some questions from Hrushovski's original paper.

Logic · Mathematics 2011-03-21 David M. Evans , Marco S. Ferreira

We present two new constructions in the usual euclidean plane. We only deal with 'Grecian Geometry', with this phrase we mean elementary geometry in the two-dimensional space R 2 . We describe and prove two propositions about 'projections'.…

Metric Geometry · Mathematics 2011-09-13 Volker Thürey

In this PhD thesis, we give a new geometric approach to higher Teichm\"uller theory. In particular we construct a geometric structure on surfaces, generalizing the complex structure, and we explore its link to Hitchin components. The…

Differential Geometry · Mathematics 2020-07-02 Alexander Thomas

We generalize Kuznetsov's theory of homological projective duality to the setting of noncommutative algebraic geometry. Simultaneously, we develop the theory over general base schemes, and remove the usual smoothness, properness, and…

Algebraic Geometry · Mathematics 2018-05-15 Alexander Perry

Recently, the authors of the present work (together with M. N. Kolountzakis) introduced a new version of the non-commutative Delsarte scheme and applied it to the problem of mutually unbiased bases. Here we use this method to investigate…

Combinatorics · Mathematics 2017-09-20 Máté Matolcsi , Mihály Weiner

A fake projective plane is a compact complex manifold of dimension 2 which has the same Betti numbers as the complex projective plane, but not isomorphic to the complex projective plane. As was shown by D. Mumford, there exists at least one…

Algebraic Geometry · Mathematics 2007-05-23 JongHae Keum

Projective Hjelmslev planes and Affine Hjelmselv planes are generalisations of projective planes and affine planes. We present an algorithm for constructing a projective Hjelmslev planes and affine Hjelsmelv planes using projective planes,…

Combinatorics · Mathematics 2015-11-05 Joanne L. Hall , Asha Rao

The paper contains a general construction which produces new examples of non simply-connected smooth projective surfaces. We analyze the resulting surfaces and their fundamental groups. Many of these fundamental groups are expected to be…

alg-geom · Mathematics 2008-02-03 Fedor Bogomolov , Ludmil Katzarkov

We examine the first order structure of pregeometries of structures built via Hrushovski constructions. In particular, we show that the class of flat pregeometries is an amalgamation class such that the pregeometry of the unbounded arity…

Logic · Mathematics 2020-06-05 Omer Mermelstein

Projective geodesic extensions are reparametrizations of the trajectories of a nonholonomic mechanical system (with only a kinetic energy Lagrangian), in such a way that they can be interpreted as part of the geodesics of a Riemannian…

Differential Geometry · Mathematics 2026-03-11 Malika Belrhazi , Tom Mestdag

We give a systematic approach to constructing non-reduced, locally Cohen-Macaulay schemes with reduced support a smooth projective variety. The hierarchy of such structures includes a lot of information about the underlying variety, its…

Algebraic Geometry · Mathematics 2007-05-23 Jon Eivind Vatne

We show that the automorphism groups of certain countable structures obtained using the Hrushovski amalgamation method are simple groups. The structures we consider are the 'uncollapsed' structures of infinite Morley rank obtained by the ab…

Logic · Mathematics 2015-09-03 David M. Evans , Zaniar Ghadernezhad , Katrin Tent

We show that the rank {\omega} structure obtained by the non-collapsed version of Hrushovski's amalgamation construction has a proper reduct. We show that this reduct is the Fra\"iss\'e-Hrushovski limit of its own age with respect to a…

Logic · Mathematics 2013-05-10 Assaf Hasson , Omer Mermelstein

This is a survey of the theory of complex projective (CP^1) structures on compact surfaces. After some preliminary discussion and definitions, we concentrate on three main topics: (1) Using the Schwarzian derivative to parameterize the…

Differential Geometry · Mathematics 2009-02-12 David Dumas

A standard procedure in classical projective geometry, using pencils of lines to extend an incidence plane to a projective plane, is examined from a constructive viewpoint. Brouwerian counterexamples reveal the limitations of traditional…

Metric Geometry · Mathematics 2024-02-05 Mark Mandelkern

We prove that the set of non-degenerate second order maximally superintegrable systems in the complex Euclidean plane carries a natural structure of a projective variety, equipped with a linear isometry group action. This is done by…

Differential Geometry · Mathematics 2017-01-31 Jonathan Kress , Konrad Schöbel

An overview is given of the various expansions of fields and fusions of strongly minimal sets obtained by means of Hrushovski's amalgamation method, as well as a characterization of the groups definable in these structures.

Logic · Mathematics 2013-09-20 Frank Olaf Wagner

We formulate and prove a weighted version of Zariski's hyperplane section theorem on the topological fundamental groups of the complements of hypersurfaces in a projective space. As an application, we calculate fundamental groups of the…

alg-geom · Mathematics 2008-02-03 Ichiro Shimada