;;; Since this is an error-checking utility, i.e. its job is to deal
;;; with screwed-up input, it'd be good style to fix it so that it can
;;; deal with circular list structure.
;;; Since this is an error-checking utility, i.e. its job is to deal
;;; with screwed-up input, it'd be good style to fix it so that it can
;;; deal with circular list structure.