(defun n+np (x n)
  ;;if x it's a multiple of n (x=n+np) --> 1 else 0.
  ;;but p>0 (p=1,2,3...)
  (check-type x integer)
  (check-type n integer)
  (locally (declare (integer  x n))
    (if (and (> x n) (zerop (mod x n))) 1 0)))