#include <bits/stdc++.h>
using namespace std;
int main() {
  int n, m;
  cin >> n >> m;
  long long int arr[n];
  fill(arr, arr + n, 0);
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < m; j++) {
      char x;
      cin >> x;
      arr[i] *= 2;
      if (x == '#') arr[i]++;
    }
  }
  for (int i = 0; i < n - 1; i++) {
    for (int j = i + 1; j < n; j++) {
      if (((long long int)(arr[i] & arr[j]) != 0) && arr[i] != arr[j]) {
        cout << "NO\n";
        return 0;
      }
    }
  }
  cout << endl;
  cout << "YES\n";
}
