Robot motion planning, weights of cohomology classes, and cohomology operations

The complexity of algorithms solving the motion planning problem is measured by a homotopy invariant $\mathrm{TC}(X)$ of the configuration space $X$ of the system. Previously known lower bounds for $\mathrm{TC}(X)$ use the structure of the cohomology algebra of $X$. In this paper we show how cohomology operations can be used to sharpen these lower bounds for $\mathrm{TC}(X)$. As an application of this technique we calculate explicitly the topological complexity of various lens spaces. The results of the paper were inspired by the work of E. Fadell and S. Husseini on weights of cohomology classes appearing in the classical lower bounds for the Lusternik-Schnirelmann category. In the appendix to this paper we give a very short proof of a generalized version of their result.