A Characterization of Motions as Bijections Preserving Inradius or Circumradius One.
A course in spatial visualisation.
A family of conics and three special ruled surfaces.
A formula for angles between subspaces of inner product spaces.
A free group of piecewise linear transformations
We prove the following conjecture of J. Mycielski: There exists a free nonabelian group of piecewise linear, orientation and area preserving transformations which acts on the punctured disk {(x,y) ∈ ℝ²: 0 < x² + y² < 1} without fixed points.
A generalization of Hermite collineation to the n-dimensional space
A Helmholtz-Lie Type Characterization of Ellipsoids, I .
A mathematical theory of origami constructions and numbers.
A non-Desarguesian space geometry
A Note of Affine Planes with Transitive Collineation Groups.
A note on a quartic with a tacnode and a flexnode
A note on ovals and their evolutoides.
A noteworthy property of the tridens curve in the isotropic plane.
A Poncelet theorem in space.
A problem on spheres in flag-spaces. (Ein Kugelproblem im Flaggenraum.)
A projective characterization of cyclicity.
A relation between the numbers of singular points and singular lines of a plane closed curve.
A souped-up version of Pardini's theorem and its application to funny curves
Abbildung der Flächen zweiten Grades nach Aehnlichkeit der Flächenelemente
Affine and projective generalization of Wallace lines.