lxml namespaces problem

[Maxim Sloyko]

Hi All!

I have a little problem with XML namespaces.
In my application I have two XML processors, that process the same
document, one after the other.  The first one looks for nodes in 'ns1'
namespace, and substitutes them, according to some algorithm. After
this processor is finished, it is guaranteed that there are no more
'ns1' nodes left in the tree. however 'ns1' namespace dclaration is
still
there, in the root node (well, I put it there manually). Now, when
this namespace is no longer needed, I want to get rid of it, because
it confuses some other processors (namely, my browser)

So, the question is, how do I do that?
del tree.getroot().nsmap['ns1']
does not seem to do the trick :(

Thanks in advance and Happy Holidays!