t‚àà  S‚ü©$</span>  for some symmetric integer matrix <code>m(s,t)</code> called the <em>Coxeter matrix</em>, where <code>m(s,t)&gt;1</code> for <code>s‚â†t</code> and <code>m(s,s)=1</code>;  <code>m(s,t)=‚àû</code> is allowed meaning there is no relation between <code>s</code> and <code>t</code>. It is true (but a non-trivial theorem) that in a Coxeter group the order  of <code>st</code> is exactly  <code>m(s,t)</code>, thus a Coxeter  group is the same as a <em>Coxeter  system</em>, that 