(assq super *built-in-classes*))
(error "in *BUILT-IN-CLASSES*: ~S has ~S as a super,~%~
but ~S is not itself a class in *BUILT-IN-CLASSES*."
(assq super *built-in-classes*))
(error "in *BUILT-IN-CLASSES*: ~S has ~S as a super,~%~
but ~S is not itself a class in *BUILT-IN-CLASSES*."