<use ,,,imports; is ,,,supertypes; -- establishing type compatibility . has ,,, subtypes; ... . >;the use.section:
. why would an interface need to import a module?
they may refer to types other than self
that are not in the top-level library .
. a supertype has or controls its subtypes;
eg, number has all of these types:
int, real, quotient, complex, modular .