#include <cstring>
#include <iostream>
#include <vector>
#include <string>
#include <map>
#include <queue>
#include <algorithm>
#include <stack>
#include <cassert>

int H, W;
char field[64][64];
bool checked[64][64];

bool judge(int dr, int dc) {
  for(int i = 0; i < H; ++i) {
    for(int j = 0; j < W; ++j) {
      checked[i][j] = false;
    }
  }
  for(int r = 0; r < H; ++r) {
    for(int c = 0; c < W; ++c) {
      if( field[r][c] != '#' ) continue;
      if( checked[r][c] ) continue;
      int nr = r + dr;
      int nc = c + dc;
      if( not ( 0 <= nr and nr < H and 0 <= nc and nc < W ) ) return false;
      if( field[r+dr][c+dc] != '#' ) return false;
      checked[r+dr][c+dc] = true;
    }
  }
  return true;
}

int main() {
  // step 1
  std::cin >> H >> W;
  for(int i = 0; i < H; ++i) {
    scanf("%s", field[i]);
  }

  // step 2
  bool flag = false;
  [&](){
    for(int r = 0; r < H; ++r) {
      for(int c = 0; c < W; ++c) {
        if( field[r][c] == '#' ) {
          flag = true;
          return;
        }
      }
    }
  }();
  if( not flag ) {
    std::cout << "NO" << std::endl;
    return 0;
  }

  // step 3
  bool res = false;
  [&](){
    for(int dr = -H + 1; dr < H; ++dr) {
      for(int dc = -W + 1; dc < W; ++dc) {
        if( dr == 0 and dc == 0 ) continue;
        if( judge(dr, dc) ) {
          res = true;
          return;
        }
      }
    }
  }();
  std::cout << (res ? "YES" : "NO") << std::endl;  
  
  return 0;
}