With Result you cannot express quantification

  The problem is that Result and U are not equivalent representation of a property.
  U is more powerful because through quantification (in the form of a continuation)
  it introduces free variables that are finally available inside the
  constructor Property.

  Result does not have this peculiar trait.

  For instance consider the property:
    Forall n ~ Property (Even n)

  Inside Property, n is available because it's in scope from the Forall's lambda.
  When considering the Set (Even n) inside property, n is an implicit metavariable.

  The closest Result representation of the above is :
    Forall N (Hold (Even ?))
  We cannot fill ? with n because it's not in scope.