#include <algorithm>
#include <cassert>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <iostream>
#include <tuple>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <ranges>
using namespace std;
using ll = long long;

auto range(int n) { return views::iota(0, n); }

template<class T, class U> ostream& operator<<(ostream& os, const pair<T, U>& p){ return os << "{" << p.first << ", " << p.second << "}"; }
template<typename T> ostream& operator<<(ostream& os, const vector<T>& obj) { os << "{"; for (const auto& e : obj) os << e << ", "; return os << "}"; }
template<typename T> ostream& operator<<(ostream& os, const set<T>& obj) { os << "set{"; for (const auto& e : obj) os << e << ", "; return os << "}"; }
template<typename T, typename U> ostream& operator<<(ostream& os, const map<T, U>& obj) { os << "map{"; for (const auto& e : obj) os << e << ", "; return os << "}"; }

#ifdef ONLINE_JUDGE
#define dump(expr) ;
#else
#define dump(expr) { cerr << "\033[33m#L" << __LINE__ << ": " << expr << "\033[39m" << endl; }
#endif

string solve() {
  int n, m; cin >> n >> m;
  vector<string> vs(n);
  for (int i : range(n)) cin >> vs[i];

  for (int vy = -n; vy <= n; ++vy) {
    for (int vx : range(m + 1)) {
      if (vx == 0 && vy == 0) continue;

      for (int i0 : range(n))
      for (int j0 : range(m)) {
        int ni = i0 - vy;
        int nj = j0 - vx;
        if (0 <= ni && ni < n && 0 <= nj && nj < m) continue;

        int count = 0;
        for (int i = i0, j = j0; 0 <= i && i < n && 0 <= j && j < m; i += vy, j += vx) {
          count += vs[i][j] == '#';
        }
        if (count % 2) goto SKIP;
      }
      dump(vy << " " << vx);
      return "YES";
SKIP:;
    }
  }
  return "NO";
}

int main() {
  cout << solve() << endl;
}