using System;
using System.Collections.Generic;
using System.Linq;

namespace Nuriwake_CS
{
    class Program
    {
        static void Main(string[] args)
        {
            Solver mysol = new Solver();
            mysol.Solve();
        }
    }

    class Solver
    {
        public void Solve()
        {
            bool ans = B.CanNuriwake();
            Console.WriteLine(ans ? "YES" : "NO");
        }

        int H, W;
        Board B;

        public Solver()
        {
            var hw = ria();
            H = hw[0];
            W = hw[1];
            string[] s = new string[H];

            for (int i = 0; i < s.Length; i++)
            {
                s[i] = rs();
            }
            B = new Board(H, W, s);

        }

        static String rs() { return Console.ReadLine(); }
        static int ri() { return int.Parse(Console.ReadLine()); }
        static long rl() { return long.Parse(Console.ReadLine()); }
        static double rd() { return double.Parse(Console.ReadLine()); }
        static String[] rsa() { return Console.ReadLine().Split(' '); }
        static int[] ria() { return Console.ReadLine().Split(' ').Select(e => int.Parse(e)).ToArray(); }
        static long[] rla() { return Console.ReadLine().Split(' ').Select(e => long.Parse(e)).ToArray(); }
        static double[] rda() { return Console.ReadLine().Split(' ').Select(e => double.Parse(e)).ToArray(); }
    }

    class Board
    {
        public enum color { Black, White, Red, Blue }

        int H, W;
        color[,] BaseBoard;
        int BlackNum;

        public Board(int h, int w, string[] s)
        {
            H = h;
            W = w;
            BlackNum = 0;
            BaseBoard = new color[H, W];
            for (int i = 0; i < h; i++)
            {
                for (int j = 0; j < w; j++)
                {
                    if (s[i][j] == '#')
                    {
                        BaseBoard[i, j] = color.Black;
                        BlackNum++;
                    }
                    else
                    {
                         BaseBoard[i,j] = color.White;
                    }
                }
            }
        }

        public bool CanNuriwake()
        {
            if(BlackNum == 0)
            {
                return false;
            }

            color[,] curBoard = new color[H, W];
            var shifts = Coordinate.MakeParallelShifts(H, W);
            foreach (Coordinate c in shifts)
            {
                curBoard = BaseCopy();
                bool ok = true;
                for (int i = 0; i < H; i++)
                {
                    for (int j = 0; j < W; j++)
                    {
                        if (curBoard[i, j] == color.Black)
                        {
                            curBoard[i, j] = color.Red;
                            try
                            {
                                if (curBoard[i + c.X, j + c.Y] == color.Black)
                                {
                                    curBoard[i + c.X, j + c.Y] = color.Blue;
                                }
                                else
                                {
                                    ok = false;
                                    break;
                                }
                            }
                            catch (Exception e)
                            {
                                ok = false;
                                break;
                            }
                        }
                    }
                    if (ok == false) break;
                }
                if (ok) return ok;
            }
            return false;
        }
        color[,] BaseCopy()
        {
            color[,] ret = new color[H, W];
            for (int i = 0; i < H; i++)
            {
                for (int j = 0; j < W; j++)
                {
                    ret[i, j] = BaseBoard[i, j];
                }
            }
            return ret;
        }
    }

    struct Coordinate
    {
        public int X, Y;
        Coordinate(int x, int y)
        {
            X = x;
            Y = y;
        }
        public static Queue<Coordinate> MakeParallelShifts(int H, int W)
        {
            Queue<Coordinate> q = new Queue<Coordinate>();
            for (int i = 0, j = 0; j < W; j++)
            {
                q.Enqueue(new Coordinate(i, j));
            }
            for (int i = 1; i < H; i++)
            {
                for (int j = -W + 1; j < W; j++)
                {
                    q.Enqueue(new Coordinate(i, j));
                }
            }
            q.Dequeue();
            return q;
        }
    }
}