#include <bits/stdc++.h>
using namespace std;
bool s[50][50];
int main() {
  int n, m;
  cin >> n >> m;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      char in;
      cin >> in;
      s[i][j] = (in == '#');
    }
  }
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      for (int p = 0; p < n - i; p++) {
        for (int q = 0; q < m - j; q++) {
          int cnt = 0;
          cnt += s[i][j] ? 1 : 0;
          cnt += s[i + p][j] ? 1 : 0;
          cnt += s[i][j + q] ? 1 : 0;
          cnt += s[i + p][j + q] ? 1 : 0;
          if (cnt != 3) {
            continue;
          } else {
            cout << "NO";
            return 0;
          }
        }
      }
    }
  }
  cout << "YES";
  return 0;
}
