(** CI Classes of MOs : active, inactive, etc *)

type mo_class =
  | Core     of int  (* Always doubly occupied *)
  | Inactive of int  (* With 0,1 or 2 holes *)
  | Active   of int  (* With 0,1 or 2 holes or particles *)
  | Virtual  of int  (* With 0,1 or 2 particles *)
  | Deleted  of int  (* Always unoccupied *)

type t 

(** Creation *)
val of_list : mo_class list -> t

val fci : ?frozen_core:bool -> MOBasis.t -> t
(** Creates the MO classes for FCI calculations : all [Active]. The 
    [n] lowest MOs are [Core] if [frozen_core = true].
*)


val core_mos : t -> int list
(** Returns a list containing the indices of the core MOs. *)

val active_mos : t -> int list
(** Returns a list containing the indices of the active MOs. *)

val virtual_mos : t -> int list
(** Returns a list containing the indices of the virtual MOs. *)

val inactive_mos : t -> int list
(** Returns a list containing the indices of the inactive MOs. *)

val deleted_mos : t -> int list
(** Returns a list containing the indices of the deleted MOs. *)


(** {2 Printers} *)

val pp_mo_occ : Format.formatter -> mo_class -> unit