"M�rio Amado Alves" <maa@liacc.up.pt> wrote in message
news:4a4de33a.0305290406.567b7451@posting.google.com...
> The pros include "naturalness" of expression, occuring both at
> creation
>
>   type Child is new Mother, Father;

This expression is very unnatural since outside hermaphroditic species a
child is by definition not substitutable for either a mother or father ;)