#include <bits/stdc++.h>
using namespace std;
set<string> A;
vector<bool> marked;
int main() {
  int n, m;
  cin >> n >> m;
  marked.resize(m);
  fill(marked.begin(), marked.end(), false);
  for (int i = 0; i < n; i++) {
    string a;
    cin >> a;
    A.insert(a);
  }
  for (auto &i : A) {
    for (int j = 0; j < m; j++) {
      if (i[j] == '#') {
        if (marked[j] == true) {
          cout << "NO" << endl;
          return 0;
        } else {
          marked[j] = true;
        }
      }
    }
  }
  cout << "YES" << endl;
  return 0;
}
