obj T1 = integer and real and string and boolean;
obj T2 = integer and real and string and boolean;
obj T3 = T1 and T2;
obj T4 = integer or string;
obj T5 = string or integer;
obj T6 = string or boolean or integer;

op Foo (t1:T1, t2:T2) = t1 = t2;

(* These should be checked, but as of 22oct99 I don't think checking of
   tuple aggregates is done yet.  17jun09 update: they appear to work now. *)
val T:T3 = { {1, 2.5, "xyz", true}, {2, 3.5, "abc", false} };
val T':T3 = [ {1, 2.5, "xyz", true}, {2, 3.5, "abc", false} ];	(* ERROR *)

op FooOr(t4:T4, t5:T5) -> boolean = (
    t4 = t5;
    t4 = 10;
    t4 = "abc";
    t4 = false;		(* ERROR (since bool is not an alternative of T4) *)
);