Write context xpath expression

Hello,
In XSL 1.0, how can I write out the XPATH expression for the current
context?  Example:

<a>
  <b>
    <c />
    <c /> <!-- assume this is the context -->
    <c />
  </b>
</a>

Assuming <c/> is the current context I would like to determine the
xpath pattern like this:
/a/b/c

How is this possible?  I get how I could walk parent;;node() but I'd
be writing the pattern backwards!
Any ideas?

Thanks,

Karl..