Maybe this is silly, but why the default dimenson of a DM is 0; why not -1?
A DM of dimension 0 is a point, while a DM of dimension -1 is a DM in a not yet complete setup state.
--
Stefano
--
What most experimenters take for granted before they begin their experiments is infinitely more interesting than any results to which their experiments lead. -- Norbert Wiener