The core? predicate determines whether its argument is a core Sol set.
(define (core? obj)
; Check against the various cases.
(case obj
; Note: SOL is not included in
; this list to avoid the
; difficulty of any other set
; including SOL.
((fundamental core explicit derived
number complex real rational integer
sstring symbol char
sset sordered unordered
pair slist
procedure
boolean) #t)
(else #f)))