On the bisectors of weakly separable sets.
On the Cayley Factorization of Calotte Conditions.
On the chiral Archimedean solids.
On the constructibility of rational angles.
On the Contact Dimension of Graphs.
On the curves of constant relative width
On the derivation of the non-Euclidean angle of parallelism function.
On the Difficulty of Triangulating Three-Dimensional Nonconvex Polyhedra.
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 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 Group of Transformations of Constructible Euclidean Planes with Preserve a Single Distance.
On the Impossibility of one Ruler-and-Compass Construction
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.