Small models for chain algebras.
Let denote the set of points with modulus one in euclidean 4-space ; and let denote the space of nonsingular vector fields on with the topology. Under what conditions are two elements from homotopic ? There are several examples of nonsingular vector fields on . However, they are all homotopic to the tangent fields of the fibrations of due to H. Hopf (there are two such classes).We construct some new examples of vector fields which can be classified geometrically. Each of these examples...
The category of quadratic algebras is endowed with a tensor structure. This allows us to construct a class of Hopf algebras studied recently under the name of quantum (semi) groups.
Let Fr(n) be the incomplete complex flag manifold of length r in Cn. We make a start on the complete determination of the torsion part of the group KO-i(Fr(n)) giving results here when r = 2, 3.
It is proved, for various spaces A, such as a surface of genus 2, a figure-eight, or a sphere of dimension ≠ 1,3,7, and for any set Σ of equations, that Σ cannot be modeled by continuous operations on A unless Σ is undemanding (a form of triviality that is defined in the paper).