public static int GetIndex(PDLPosUnaryConstructor op)
        {
            switch (op)
            {
            case PDLPosUnaryConstructor.Pred: return(0);

            case PDLPosUnaryConstructor.Succ: return(1);

            default: throw new PDLException("undefined operator");
            }
        }
 public static int GetIndex(PDLPosUnaryConstructor op)
 {
     switch (op)
     {
         case PDLPosUnaryConstructor.Pred: return 0;
         case PDLPosUnaryConstructor.Succ: return 1;
         default: throw new PDLException("undefined operator");
     }
 }