so that (TYPEP (MAKE-ARRAY 3) '(VECTOR SOMETHING-NOT-DEFINED-YET))
returns (VALUES T T). Probably it should be an error instead,
complaining that the type SOMETHING-NOT-DEFINED-YET is not defined.
+ Or perhaps UPGRADED-ARRAY-ELEMENT-TYPE should just fail when a type
+ isn't defined yet. (What if the definition of
+ SOMETHING-NOT-DEFINED-YET turns out to be SINGLE-FLOAT?)
41:
TYPEP of VALUES types is sometimes implemented very inefficiently, e.g. in