On the Erdös-Debrunner inequality.
On the existence and constructibility of inscribed polygons.
On the existence of triangle with given angle and opposite angle bisectors length.
On the finite blocking property
A planar polygonal billiard is said to have the finite blocking property if for every pair of points in there exists a finite number of “blocking” points such that every billiard trajectory from to meets one of the ’s. Generalizing our construction of a counter-example to a theorem of Hiemer and Snurnikov, we show that the only regular polygons that have the finite blocking property are the square, the equilateral triangle and the hexagon. Then we extend this result to translation surfaces....
On the fixed point of a collineation of the real projective plane.
On the foundation of geometry.
On the functional equation ... (Short Communication).
On the fundamental group of the fixed points of an unipotent action.
On the generalized stereographic projection.
On the geometric relation of twin-points of the triangle. (Zur Verwandtschaft der Zwillingspunkte beim Dreieck.)
On the geometry of field extensions.
On the geometry of symplectic involutions.
On the graphs of Hoffman-Singleton and Higman-Sims.
On the Group of Transformations of Constructible Euclidean Planes with Preserve a Single Distance.
On the Haagerup inequality and groups acting on -buildings
Let be a group endowed with a length function , and let be a linear subspace of . We say that satisfies the Haagerup inequality if there exists constants such that, for any , the convolutor norm of on is dominated by times the norm of . We show that, for , the Haagerup inequality can be expressed in terms of decay of random walks associated with finitely supported symmetric probability measures on . If is a word length function on a finitely generated group , we show that,...
On the history of generalized quadrangles.
On the Impossibility of one Ruler-and-Compass Construction
On the incidence structures of polar spaces and quadrics.
On the Infinite Loch Ness monster
In this paper we introduce the topological surface called {Infinite Loch Ness monster}, discussing how this name has evolved and how it has been historically understood. We give two constructions of this surface, one of them having translation structure and the other hyperbolic structure.
On the integral geometry of the linear subspaces in a biplanar space