- (not=? [ compare ] [ x y ])procedure
If the values x and y are given, test if x and y are in the relation specified by the name of the procedure rel?, with respect to compare procedure compare; otherwise construct a predicate procedure.
In the forms (rel? [ compare ] x y), the result is a boolean (either #t or #f) depending on (compare x y) and the test rel? as specified for if<? etc. If compare is not supplied, default-compare is used.
In the form (rel? [ compare ]), the predicate procedure (lambda (x y) (rel? compare x y)) is constructed. Again, if compare is not supplied, default-compare is used.