Homology and derived series of groups.
A homology lens space is a closed 3-manifold with ℤ-homology groups isomorphic to those of a lens space. A useful theorem found in [Fu] states that a homology lens space may be obtained by an (n/1)-Dehn surgery on a homology 3-sphere if and only if the linking form of is equivalent to (1/n). In this note we generalize this result to cover all homology lens spaces, and in the process offer an alternative proof based on classical 3-manifold techniques.
A homology theory is developed for set-theoretic Yang-Baxter equations, and knot invariants are constructed by generalized colorings by biquandles and Yang-Baxter cocycles.
Using Fox differential calculus, for any positive integer , we construct a map on the mapping class group of a surface of genus with one boundary component, such that, when restricted to an appropriate subgroup, it coincides with the Johnson-Morita homomorphism. This allows us to construct very easily a homomorphic extension to of the second and third Johnson-Morita homomorphisms.