{ka'e nu} versus {du'u}

["And Rosta" <a.rosta@lycos.co.uk>]

If {du'u} were abolished, are there any cases where it could not
be replaced by {ka'e nu}, assuming an appropriate tweaking of
the semantics of sumti places that take a du'u sumti (e.g.
"true" being reconstrued as "is actual", is "ca'a nu")?

I am beginning to think that the meaning that I generally
express by {lo'e du'u} and that others generally express by
{le nu} could/should be expressed by {lo'e ka'e nu} (or
sometimes {lo(i) ca'a nu}).

--And.