Implicit constraints in type declaration

[Alain Frisch <frisch@clipper.ens.fr>]

Hello,

I don't understand why the following type declaration implies a
constraint:

# type 'a t = int and b = int t;;
type 'a t = int constraint 'a = int
type b = int t

Also, I don't understand this error message (I can imagine why
the declaration is illegal):

# type 'a t = u and u = int;;
                    ^^^^^^^
A type variable is unbound in this type declaration


-- 
  Alain Frisch