structural subtype polymorphism

4.25: adda/oop/structural subtype polymorphism:
. in addition to polymorphs and evolvers
there are generals, where type is not named;
instead,
the given obj' must support the same operations
as expected by the formal symbol
that the obj' was assigned to;
and, in order to show
where it's getting this support from,
the obj' must carry a type.tag;
this would be in addition to
a possible subtype tag that the type'mgt would use
to discriminate between a polymorph's subtypes .