All the built-in types except for "any" have "equal", "similar", "copy", and "unparse" methods. These methods are optional for the parameterized types such as "array[T]": an instantiation will have one of these methods only if each of the actual parameter types has the method.
None of the built-in types and parameterized types can have subtypes, except for "any", which is the supertype of all types. There is no type hierarchy relating any of the other built-in types, except that there is a rich hierarchy for routine types.
The built-in types and parameterized types are implemented by classes that cannot be subclassed.
The Theta environment contains a number of equates that describe various properties and limitations of the built-in types. The corresponding type definitions in this Appendix describe these equates in more detail.