#include <bits/stdc++.h>

using namespace std;

int main(int argc, const char *argv[]) {
  int h, w;
  cin >> h >> w;
  vector<string> grid(h);
  for (int i = 0; i < h; ++i) {
    cin >> grid[i];
  }

  bool ans = false;
  for (int i = 0; i <= h && !ans; ++i) {
    for (int j = 0; j <= w && !ans; ++j) {
      if (i + j == 0) {
        continue;
      }

      bool ok = true;
      vector<vector<bool>> used(h, vector(w, false));
      for (int y = 0; y < h && ok; ++y) {
        for (int x = 0; x < w && ok; ++x) {
          char c = grid[y][x];
          if (c != '#' || used[y][x]) {
            continue;
          }

          int x2 = x + j, y2 = y + i;
          if (x2 >= w || y2 >= h || grid[y2][x2] != '#' || used[y2][x2]) {
            ok = false;
            break;
          }

          used[y2][x2] = true;
          used[y][x] = true;
        }
      }

      if (ok) {
        ans = true;
      }
    }
  }

  cout << (ans ? "YES" : "NO") << '\n';
}