[Grace-core] Built-in egality

[Marco Servetto]

>A confidential field (or method) can only be accessed from within the
>object. It is not part of the public type but is part of the representation.
I "know this definition" but for the best of my understanding is not coherent.
grace have closures, so an object created inside another object can
still see confidential stuff, and thus, is unclear to me when two
objects are structurally subtype of one other.

A coherent solution should be that non public stuff can "only" be
referred by the sintactically enclosed name, if you can access by
this/self it starts to get weird.
Is it true that for every variable (including this/self) I can define
a variable with dynamic/unknown  type and use such variable as it was
this/self?