using System;

namespace yukicoder
{
    class _179
    {
        static void Main()
        {
            int[] hw = Array.ConvertAll(Console.ReadLine().Split(' ')
               , x => int.Parse(x));
            int h = hw[0];
            int w = hw[1];
            bool[,] b = new bool[h, w];
            for (int i = 0; i < h; i++)
            {
                string iw = Console.ReadLine();

                for (int j = 0; j < w; j++)
                {
                    char ij = iw[j];

                    b[i, j] = ij == '#';
                }
            }

            int i0 = -1;
            int j0 = -1;
            for (int i = 0; i < h; i++)
            {
                for (int j = 0; j < w; j++)
                {
                    if(b[i,j])
                    {
                        if (i0 == -1 && j0 == -1)
                        {
                            i0 = i;
                            j0 = j;
                        }
                        else
                        {
                            int hd = i - i0;
                            int wd = j - j0;

                            if (isp(h, w, (bool[,])b.Clone(), hd, wd))
                            {
                                Console.WriteLine("YES");
                                return;
                            }
                        }
                    }
                }
            }

            Console.WriteLine("NO");
        }

        static bool isp(int h, int w, bool[,] b, int hd, int wd)
        {
            for (int id = 0; id < h; id++)
            {
                for (int jd = 0; jd < w; jd++)
                {
                    if (b[id, jd])
                    {
                        if (id + hd < 0 || jd + wd < 0
                            || id + hd > h - 1 || jd + wd > w - 1)
                        {
                            return false;
                        }
                        if (b[id + hd, jd + wd])
                        {
                            b[id + hd, jd + wd] = false;
                        }
                        else
                        {
                            return false;
                        }
                    }
                }
            }
            return true;
        }
    }
}