Comma Separated Values - XSLT1.0

Hi,

I have 2 XML elements each containing comma separated values. I need to
take each individual value from <elem2> and see if it exists in <elem1>. If
true is returned, go off and do something..... otherwise get the next value
from <elem2> and compare it to all the values in <elem1> etc etc.

<data>
      <elem1>bloggs,smith,jones,bush,howard,bennis</elem1>
      <elem2>skeen,seinfield,longshaw,bloggs,keitel</elem2>
</data>


So the approach would be:

Take 'skeen' and compare it to all the comma separated values in <elem1>.
If FALSE is returned, take 'seinfield' and compare to all values in <elem1>
and so on...If TRUE is returned at any stage DO SOMETHING. If at the end
nothing is found, DO SOMETHING DIFFERENT......


Any suggestions on how to do this?

Thanks!