datatype t = C of t;datatype 'a u = D of 'a;datatype ('a,'b) v = E of ('a * 'b); signature S = sig         datatype t = C of t 	datatype 'a u = D of 'a;	datatype ('a,'b) v = E of ('a * 'b)end; signature Ok = S where type t = t and type 'a u = 'a u and type ('a,'b) v = ('a,'b) v; signature FailWeirdButValidSML = S where type t = int;signature Fail = S where type t = int * int; signature FailWeirdButValidSML = S where type 'a u = 'a list;signature Fail = S where type 'a u = int u;signature Fail = S where type 'a u = 'a * 'a; datatype ('a,'b) w = W;type ('a,'b,'c) x = ('a,'b) w;type ('a,'b) y = ('a,'a) w;signature FailWeirdButValidSML = S where type ('a,'b) v = ('a,'b) w;signature FailWeirdButValidSML = S where type ('a,'b) v = ('a,'b,int) x;signature Fail = S where type ('a,'b) v = ('a,'a)w;signature Fail = S where type ('a,'b) v = ('a,'a)w;signature Fail = S where type ('a,'b) v = ('a,'b)y; datatype t = C of bool | D of int; signature Fail = sig datatype u = C of bool end where type u = t; signature Fail = sig datatype u = C of bool | D of bool end where type u = t; signature Fail = sig datatype u = C of bool | D of int end where type u = int; signature OK = sig datatype u = C of bool | D of int end where type u = t; (* check indirections in the realization *) type s = t; signature Fail = sig datatype u = C of bool end where type u = s; signature Fail = sig datatype u = C of bool | D of bool end where type u = s; signature OK = sig datatype u = C of bool | D of int end where type u = s; (* check indirections in the spec *) signature Fail = sig datatype u = C of bool type v = u end where type v = t; signature Fail = sig datatype u = C of bool | D of bool type v = u end where type v = t; signature OK = sig datatype u = C of bool | D of int type v = u end where type v = t; (* the reason we reject more where type constraints than SML is to preclude elaboration of the following *)local datatype t = C of int;      signature Fail = sig datatype u = C of bool end where type u = t;      structure X = rec(X:S)struct datatype u = datatype X.u end       val X.C b = C 0in end;