arXiv subjects
Publications and source records attributed to Robert B. Howlett.
We further develop the theory of $W\!$-graph ideals, first introduced by the authors in reference [6]. We discuss $W\!$-graph subideals, and induction and restriction of $W\!$-graph ideals for parabolic subgroups. We introduce $W\!$-graph biideals: those $W\!$-graph ideals that yield $(W\times W^{\mathrm o})$-graphs, where $W^{\mathrm o}$ is the group opposite to $W$. We determine all $W\!$-graph ideals and biideals in finite Coxeter groups of rank 2.
We introduce a concept of a W-graph ideal in a Coxeter group. The main goal of this paper is to describe how to construct a W-graph from a given W-graph ideal. The principal application of this idea is in type A, where it provides an algorithm for the construction of W-graphs for Specht modules.
By studying the action of the Weyl group of a simple Lie algebra on its root lattice, we construct torsion free subgroups of small and explicitly determined index in a large infinite class of Coxeter groups. One spin-off is the construction of hyperbolic manifolds of very small volume in up to 8 dimensions.