object X =  A and B and C;
object Y extends X =  D and E;
object Z extends X =  E and F and G;

obj A;
obj B;
obj C;
obj D;
obj E;
obj F;
obj G;

object XL =  X*;

function CheckForYinXL(xl:XL, y:Y)->boolean = (
    (y in xl)				(* OK as of 29nov01, since we've
					 * changed (i.e., fixed) chkIn to use
					 * assmntCompat instead of just plain
					 * compat.

					 * Prior to 29nov1 it was an error,
					 * since we could not check directly
					 * for a Y in an XL. *)
	or

    (exists (x in xl) (x.<Y = y))	(* OK, since we down-cast explicitly *)

	or

    (exists (x in xl)			(* OK, but x?<Y check is not *)
	x?<Y and (x.<Y = y))		(* necessary here to achieve the
					 * desired result, since x.<Y will fail
					 * in all the right places.  This
					 * should be explained carefully in the
					 * manual. *)
);


function CheckPolymorphicEqualityYetAgain(x:X, y:Y, z:Z)->boolean = (

    (x = y)		(* ERROR *)
	or
    (x = z)		(* ERROR *)
	or
    (y = z)		(* ERROR *)
	or
    (x.<Y = y)		(* OK, but note potential semantic ambiguity in that 
			 * '=' could fail either because x.<Y fails, or because
			 * x.Y is actually not = to y. *)
);