> I need to change a namaspaces because i need to post this xml in a 
> webservices that recognize only with e namespaces and nillable tag.

Odd, it can't be using a namespace-compliant xml parser then otherwise
the prefix would make no difference.

> Now your xsl zap the empty tag but no namespaces insert, now my output 
> is with your sylesheets:

In theory the xsl processor is allowed to ignore the request to use the
cup: prefix and use another prefix, or no prefix(as the prefix is considered
unimportant) but I have not seen an xsl processor do that. saxon gave
the output I showed on the input that you posted which does use the cup
prefix. What processor are you using?

David