A Subset_of_function is a Specialisation_of_class that is between two instances of Maths_function (superclass and subclass); and that indicates the all the members of the subclass are also members of the superclass.
NOTE - The domain of the subclass Maths_function is a subset of the domain of the superclass Maths_function.
Within their common domain, the subclass and the superclass instances of Maths_function are identical.
EXPRESS specification:
*) ENTITY Subset_of_function SUBTYPE OF (Specialisation_of_class); subclass : Maths_function; superclass : Maths_function; END_ENTITY; (*
Attribute definitions:
subclass: the Maths_function that consists entirely of members of the superclass.
superclass: the Maths_function that contains all members of the subclass.