(simple?) xpath question

All *help*!
 
What is the best way to query xml with xpath to get a disjoint nodelist?
Specifically i want to include just the root node alongwith a descendent node.
 
XML:
 
<a>
  <b>
    <c>
    </c>
 </b>
</a>
 
XPATH:
 
//c
 
DESIRED RESULT NODELIST:
i.e. not this:
<c>
</c>
 
but rather this:
<a>
  <c>
  </c>
</a>