module type MyHash  =
  sig
    include module type of struct include Hashtbl end
    val replace : ('a, 'b) t -> 'a -> 'b -> unit (a:3)
  end
module type MyHash  =
  sig
    include ((module type of struct include Hashtbl end)[@onModuleTypeOf ])
    val replace : ('a, 'b) t -> 'a -> 'b -> unit (a:3)
  end