Arseniy Akopyan

ANY CYCLIC QUADRILATERAL CAN BE INSCRIBED IN ANY CLOSED CONVEX SMOOTH CURVE

We prove that any cyclic quadrilateral can be inscribed in any closed convex

The extremal spheres theorem

C^1

Elementary results in non-reflexive Finsler billiards

-curve. The smoothness condition is not required if the quadrilateral is a rectangle.

Bang's problem and symplectic invariants

Consider a polygon P and all neighboring circles (circles going through three consecutive vertices of P). We say that a neighboring circle is extremal if it is empty (no vertices of P inside) or full (no vertices of P outside). It is well known that for any convex polygon there exist at least two empty and at least two full circles, i.e. at least four extremal circles. In 1990 Schatteman considered a generalization of this theorem for convex polytopes in d-dimensional Euclidean space. Namely, he claimed that there exist at least 2d extremal neighboring spheres for generic polytopes. His proof is based on the Bruggesser-Mani shelling method. In this paper, we show that there are certain gaps in Schattemans proof. We also show that using the Bruggesser-Mani-Schatteman method it is possible to prove that there are at least d+1 extremal neighboring spheres. However, the existence problem of 2d extremal neighboring spheres is still open.