make Qc_of_Z not a Coercion any more
This implements #102 for Qc_of_Z
-- Qc
is not a widely used type (any more) so I think the fallout from this should be quite limited.
This implements #102 for Qc_of_Z
-- Qc
is not a widely used type (any more) so I think the fallout from this should be quite limited.