#include <bits/stdc++.h>
using namespace std;
int visited[100];
int main() {
  int n, m;
  cin >> n >> m;
  string s[n];
  for (int i = 0; i < n; i++) cin >> s[i];
  for (int i = 0; i < m; i++) {
    string str = "";
    for (int j = 0; j < n; j++) {
      if (s[j][i] == '#') {
        if (str == "") {
          str = s[j];
        } else if (str != s[j]) {
          cout << "NO";
          return 0;
        }
      }
    }
  }
  cout << "YES";
}
