is a pair <code>(W,S)</code> of a group <code>W</code> and a set <code>S‚äÇW</code> of involutions,  such  that  the  group  is  presented  by  generators <code>S</code> and relations describing the order of the product of two elements of <code>S</code>.</p><p>A   Coxeter   group   has   a   natural   representation,  its  <em>reflection representation</em>, on a real vector space <code>V</code> of dimension <code>length(S)</code> (which is  the  <em>Coxeter  rank</em>  of  W),  where  each  element  of