+(define-public (number-pair-list? x)
+ (and (list? x)
+ (every number-pair? x)))
+
+(define-public (fraction? x)
+ (and (pair? x)
+ (index? (car x)) (index? (cdr x))))
+
+(define-public (rational-or-procedure? x)
+ (or
+ (and (rational? x) (exact? x))
+ (procedure? x)))
+