Some recent applications of ultrafilters to topology
Several years ago, we discussed the problem of approximation polynomials with Milan Práger. This paper is a natural continuation of the work we collaborated on. An important part of numerical analysis is the problem of finding an approximation of a given function. This problem can be solved in many ways. The aim of this paper is to show how interpolation can be combined with the Chebyshev approximation.
Motivated by the study of CR-submanifolds of codimension in , the authors consider here a -dimensional oriented manifold equipped with a -dimensional distribution. Under some non-degeneracy condition, two different geometric situations can occur. In the elliptic case, one constructs a canonical almost complex structure on ; the hyperbolic case leads to a canonical almost product structure. In both cases the only local invariants are given by the obstructions to integrability for these structures....
The mathematicians’ Digital mathematics library (DML) summarises the generous project that all mathematics ever published should end up in digital form so that it would be more easily referenced, accessed, used. This concept was formulated at the very beginning of this century, and yielded a lot of international activity that culminated around years 2002–2005. While it is estimated that a substantial part of the existing math literature is already available in some digital format, nothing looking...