sig
type t = Skel.point option array
val empty : int -> 'a option array
val iter : ('a -> unit) -> 'a option array -> unit
val fold : ('a -> 'b -> 'a) -> 'a -> 'b option array -> 'a
val map : ('a -> 'b) -> 'a option array -> 'b option array
val length : (float * float * float) option array -> float
val add :
(float * float * float) option array ->
(float * float * float) option array ->
(float * float * float) option array
val sub :
(float * float * float) option array ->
(float * float * float) option array ->
(float * float * float) option array
end