INTERFACE M3SetVal;

TYPE
  T <: REFANY;

PROCEDURE NewEmpty      (n_elts: INTEGER): T;
PROCEDURE Compare       (a, b: T): INTEGER;
PROCEDURE Union         (a, b: T): T;
PROCEDURE Intersection  (a, b: T): T;
PROCEDURE Difference    (a, b: T): T;
PROCEDURE SymDifference (a, b: T): T;
PROCEDURE Include       (set: T;  elt: INTEGER): T;
PROCEDURE Exclude       (set: T;  elt: INTEGER): T;
PROCEDURE IsMember      (set: T;  elt: INTEGER): BOOLEAN;

END M3SetVal.

Compare(a, b) returns -1 if a < b, 0 if a = b, +1 if a > b, and -99 otherwise.

If the two sets passed to any of these functions differ in size, NIL is returned.

All sets are zero-based. That is, they are sets of [0..n].