Proper Subtype & Supertype
A proper subtype is (strictly) more specific than a given type, and a proper supertype is (strictly) more general than a given type.
A type is never either a proper subtype nor a proper supertype of itself.
The proper subtype/proper supertype relationship can be tested by running the Boolean-returning methods
"_⊃_". In the first method, the suspected proper subtype is passed as the left-hand argument, and the suspected proper supertype as the right-hand argument. For the second method, the argument positions are switched. Note that the characters used to establish the proper subtype/proper supertype relationships are the Unicode "subset of" and "superset of" characters. This is because Avail types are sets, and entities acquire type membership by meeting the characteristics of a member of the set.
See also: Subtype & Supertype