My problem ist that there might be different contexts, in which the
two stylesheet-modules are used. So there might be a stylesheet C,
using some xsl:keys of A, without importing B, because it don't needs
it directly. Stylesheet D imports only B, because it uses no key of A.
In this case I would have to keep in mind, that they depend on each
other, so that importing one of them requires to import the other,
too.
Or I have to guarantee that one of the stylesheets is never used
without the other, so that I can import the other in this stylesheet.