#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
#include <bitset>
#include <iomanip>
#include <sys/time.h>
#include <tuple>
#include <random>
using namespace std;

#define endl '\n'
#define ALL(v) (v).begin(), (v).end()
#define RALL(v) (v).rbegin(), (v).rend()
#define UNIQ(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef long double ld;
typedef pair<int, int> P;
typedef complex<double> comp;
typedef vector< vector<ld> > matrix;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};
const int inf = 1e9 + 9;
const ll mod = 1e9 + 7;
const double eps = 1e-8;
const double pi = acos(-1);

int h, w;
string s[55];

bool used[55][55];

bool check(int p, int q) {
    memset(used, false, sizeof(used));
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            if ((i + p >= h || j + q >= w) && s[i][j] == '#' && !used[i][j]) return false;
            if (i + p < h && j + q < w && s[i][j] == '#' && !used[i][j]) {
                if (s[i+p][j+q] == '#') used[i+p][j+q] = true;
                else return false;
            }
        }
    }
    return true;
}

bool solve() {
    for (int i = 0; i < h; i++) {
        for (int j = 0; j < w; j++) {
            if (i == 0 && j == 0) continue;
            if (check(i, j))
                return true;
        }
    }
    return false;
}

void input() {
    cin >> h >> w;
    for (int i = 0; i < h; i++) cin >> s[i];
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    input();
    cout << (solve()?"YES":"NO") << endl;
}