let iters1 max_iter xc yc =
  let rec aux count x y =
    if count = max_iter then max_iter else begin
      if x *. x  +. y *. y >= 4.0 then count else
      aux (count+1) (x *. x -. y *. y +. xc) (2.0 *. x *. y +. yc)
    end in
  aux 0 xc yc