XPath to search for elements in a sequence

With XML similar to:

< a >
< b >
< c > 1 </ c >
< c > 2 </ c >
< c > 3 </ c >
</ b >

I'm trying to create an xpath expression (for a postgresql query) that will return if is a particular value and not that is all three values.

What I currently have (which does not work) is:

select * from someTable where xpath ('//uim:a/text()', job, ARRAY[ ARRAY['uim',' http://www.cmpy.com/uim '] ])::text[] IN (ARRAY['1','3']);

If I try with ARRAY['1'] this will not return any values but with ARRAY['1','2','3'] it will return all three.

How can I select based on a single element in a sequence?

Thanks.