 a <em>reduced word</em>  for <code>w</code>. The main property of  reduced words is the <em>exchange lemma</em> which  states that if <code>s‚ÇÅ‚Ä¶s‚Çñ</code> is a reduced word for <code>w</code> (thus <code>k=l(w)</code>) and <code>s‚àà  S</code> is such that <code>l(sw)‚â§l(w)</code> then one  of the <code>s·µ¢</code> in the word for <code>w</code> can be deleted to obtain a reduced word for <code>sw</code>. Thus given <code>s‚àà S</code> and <code>w‚àà W</code>,  either <c