Objects that Cannot Be Taken Apart with Two Hands.
Hyperbolic virtual polytopes arose originally as polytopal versions of counterexamples to the following A.D.Alexandrov’s uniqueness conjecture: Let K ⊂ ℝ3 be a smooth convex body. If for a constant C, at every point of ∂K, we have R 1 ≤ C ≤ R 2 then K is a ball. (R 1 and R 2 stand for the principal curvature radii of ∂K.) This paper gives a new (in comparison with the previous construction by Y.Martinez-Maure and by G.Panina) series of counterexamples to the conjecture. In particular, a hyperbolic...
The Blaschke–Kakutani result characterizes inner product spaces , among normed spaces of dimension at least 3, by the property that for every 2 dimensional subspace there is a norm 1 linear projection onto . In this paper, we determine which closed neighborhoods of zero in a real locally convex space of dimension at least 3 have the property that for every 2 dimensional subspace there is a continuous linear projection onto with .
This paper follows the article by V. Medek which solves the problem of finding the boundary of a convex polyhedron in both parallel and central projections. The aim is to give a method which yields a simple algorithm for the automation of an arbitrary graphic projection of a convex polyhedron. Section 1 of this paper recalls some necessary concepts from the graph theory. In Section 2 graphs are applied to determine visibility of a convex polyhedron.