(list? 'a) ⇒ #f
(list? '(a b)) ⇒ #t
(list? (cons 'a (cons 'b '()))) ⇒ #t
(list? (cons 'a 'b)) ⇒ #f [not a true list]
member tests whether its first argument is a member of its second
argument:
(member 3 '(1 2 3 4 5)) ⇒ (3 4 5) [recall any non-#f value is true]
(member 7 '(1 2 3 4 5)) ⇒ #f
(member 3 "1 2 3 4 5") ⇒ Error - member: not a proper list: "1 2 3 4 5"