- (>=/>=? [ compare ] [ x y z ])procedure
Test if x, y, and z form a chain with the two relations specified by the name of the procedure rel1/rel2?, with respect to the compare procedure compare.
If compare is not provided, default-compare is used. If x y z are not provided, a predicate procedure of three arguments is constructed. The order in which the values are compared is unspecified, but each value is compared at least once.