typespec—a type specifier.
environment—an environment object.
The default is nil, denoting the null lexical environment
and the and current global environment.
upgraded-typespec—a type specifier.
upgraded-complex-part-type returns the part type of the
most specialized complex number representation that can
hold parts of type typespec.
The typespec is a subtype of (and possibly type equivalent to) the upgraded-typespec.
The purpose of upgraded-complex-part-type
is to reveal how an implementation does its upgrading.
complex (Function) (function and type)