Räumliche Zindlerkurven.
Reconstructing Plane Sets from Projections.
Reduced spherical polygons
For every hemisphere K supporting a spherically convex body C of the d-dimensional sphere we consider the width of C determined by K. By the thickness Δ(C) of C we mean the minimum of the widths of C over all supporting hemispheres K of C. A spherically convex body is said to be reduced provided Δ(Z) < Δ(R) for every spherically convex body Z ⊂ R different from R. We characterize reduced spherical polygons on S². We show that every reduced spherical polygon is of thickness at most π/2. We...
Relative isodiametric inequalities.
Relative Newton Numbers.
Representation of curves of constant width in the hyperbolic plane.
Rigidity and Energy.
Rotation indices related to Poncelet’s closure theorem
Let CRCr denote an annulus formed by two non-concentric circles CR, Cr in the Euclidean plane. We prove that if Poncelet’s closure theorem holds for k-gons circuminscribed to CRCr, then there exist circles inside this annulus which satisfy Poncelet’s closure theorem together with Cr, with ngons for any n > k.