Sorry to correct myself:

On Sat, May 22, 2010 at 10:24 PM, Carlos Camarao <carlos.camarao@gmail.com> wrote:
...
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PS: I think that a definition of orphan/non-orphan instance definition
for MPTCs should be different.
Letting:  ...
   instance-def(I,C,M,tv) = I is an instance definition of class C, occurring in
                              module M, that instantiates class variable tv
 
Should be: instance-def(I,C,M,tv,T) = I is an instance def of class C, occurring in
                                  module M, that instanticates class variable tv to datatype T
and replace occurrences of instance-def(I,C,M,tv) to instance-def(I,C,M,tv,T).

And I think a correct definition of orphan/non-orphan for MPTCs should 
be along the line:
...
That is, an instance should be considered non-orphan if there exists
at least one datatype to which a class type variable in such instance
is instantiated, because other instances which instantiate such class
type variable to such datatype would be non-orphan.
                                                                             ^^^^     (delete "non-".)
 ... type variable to such datatype would be orphan.

Cheers,

Carlos