For a finite group  <I>G</i>  and  set of generators <I>S </i> of <I> G</I>
a directed graph
Cay(<i>S</I>:<i>G</i>)
is defined as follows:<br>
1.      Each element of <I>G</i> is a vertex of  Cay(<i>S</I>:<i>G</i>).<br>
2.      For each <I>x</i> and <i>y</i> in <i>G</i>, there is an arc from <i>x</i> to <i>y</i> if and only if <i>xs = y</i>  for some <I>s &#8712 S</i> .