functor F X:sig type t end = struct datatype u = C of X.t ref end structure  A = F (struct type t = unit end);val ok = op = : A.u * A.u -> bool; structure  B = F (struct type t = unit -> unit end);val ok = op = : B.u * B.u -> bool; functor G X:sig type t end = struct datatype u = C of X.t end;structure C = G(struct type t = unit end);val fail = op = : C.u * C.u -> bool;structure D = G(struct type t = unit -> unit end);val fail = op = : D.u * D.u -> bool; functor H X:sig eqtype t end = struct datatype u = C of X.t end;structure E = H(struct type t = unit end);val ok = op = : E.u * E.u -> bool; functor I X:sig type s eqtype t end = struct datatype u = C of X.t end;structure F = I(struct type s = unit type t = unit end);val ok = op = : F.u * F.u -> bool;structure G = I(struct type s = unit -> unit type t = unit end);val ok = op = :G.u * G.u -> bool;  functor ok(F:functor X:sig type t end -> sig eqtype u end) =    op F:functor X:sig type t end -> sig eqtype u end; (* test contra-variant domain *)functor ok(F:functor X:sig type t end -> sig eqtype u end) =    op F:functor X:sig eqtype t end -> sig eqtype u end; (* test co-variant range *)functor ok(F:functor X:sig type t end -> sig eqtype u end) =    op F:functor X:sig type t end -> sig type u end; (* test contra-variant domain and  co-variant range *) functor ok(F:functor X:sig type t end -> sig eqtype u end) =    op F:functor X:sig eqtype t end -> sig type u end; (* test co-variant domain fails *)  functor fail(F:functor X:sig eqtype t end -> sig type u end) =    op F:functor X:sig type t end -> sig type u end; (* test contra-variant range fails *) functor fail(F:functor X:sig eqtype t end -> sig type u end) =    op F:functor X:sig eqtype t end -> sig eqtype u end;