#include <bits/stdc++.h>
using namespace std;
using ll = long long;
void solve() {
  ll n, m;
  cin >> n >> m;
  string s[50];
  bool check[50];
  for (ll i = 0; i < n; i++) {
    cin >> s[i];
    check[i] = true;
  }
  vector<vector<ll> > c;
  for (ll i = 0; i < m; i++) {
    vector<ll> temp;
    c.push_back(temp);
    for (ll j = 0; j < n; j++) {
      if (s[j][i] == '#' && check[j] == true) {
        c[i].push_back(j);
        check[j] == false;
      }
    }
  }
  ll flag = 0;
  for (ll j = 0; j < m; j++) {
    for (ll i = 1; i < c[j].size(); i++) {
      if (s[c[j][i]] != s[c[j][i - 1]]) {
        flag = 1;
        break;
      }
    }
    if (flag == 1) {
      break;
    }
  }
  if (flag == 1)
    cout << "NO\n";
  else
    cout << "YES\n";
}
int main() {
  ll t = 1;
  while (t--) {
    solve();
  }
  return 0;
}
