module Face = struct
let newf gd1 gd2 perm = let n =

end;;

module type Zonep = sig
    exception BadIn
    val newz :
      float array array ->
      (float array -> float array -> float -> 'a) array ->
      float array array * (int -> float -> float array -> float array -> 'a)
  end;;
module type Facetp = sig
   val ray : wh -> vel -> int
end;;

module Z = (Zone : Zonep);;