type t =
| Pos 
| Neg

let of_nperm nperm =
  if (nperm land 1) = 1 then Neg
  else Pos

let add_nperm phase = function
  | 0 -> phase
  | nperm ->
    begin
      match (phase, of_nperm nperm) with
      | (Pos,Pos) | (Neg,Neg) -> Pos
      | _ -> Neg
    end


let pp_phase ppf = function
  | Pos -> Format.fprintf ppf "@[<h>+1@]"
  | Neg -> Format.fprintf ppf "@[<h>-1@]"