type t 
val zero : t
val of_float_triplet : float * float * float -> [< `Angstrom | `Bohr ] -> t
val of_3_floats : float -> float -> float -> [< `Angstrom | `Bohr ] -> t
val to_string : t -> string
val x : t -> float 
val y : t -> float 
val z : t -> float 
val coord : t -> int -> float 
val to_float_array : t -> float array
val (|-) : t -> t -> t
val (|+) : t -> t -> t
val (|.) : float -> t -> t
val dot  : t -> t -> float
val to_Angstrom : t -> t
val to_Bohr : t -> t
val norm : t -> float