#include <bits/stdc++.h>

using namespace std;

const string yes = "YES";
const string no = "NO";

const int MAX = 55;
int h, w;
char S[MAX][MAX];
bool vis[MAX][MAX];

inline bool in(const int hh, const int ww) {
    return 0 <= hh && hh < h && 0 <= ww && ww < w;
}

int main() {
    scanf("%d%d", &h, &w);
    {
        bool valid = false;
        for (int i = 0; i < h; i++) {
            scanf("%s", S[i]);
            for (int j = 0; j < w; j++) {
                valid |= S[i][j] == '#';
            }
        }
        if (!valid) {
            cout << no << endl;
            return 0;
        }
    }
    for (int i = -h; i <= h; i++) {
        for (int j = -w; j <= w; j++) {
            if (i == 0 && j == 0) {
                continue;
            }
            bool ok = true;

            memset(vis, false, sizeof(vis));
            for (int k = 0; k < h; k++) {
                for (int l = 0; l < w; l++) {
                    if (S[k][l] == '#' && !vis[k][l]) {
                        if (!in(k + i, l + j) || S[k + i][l + j] == '.' || vis[k + i][l + j]) {
                            ok = false;
                        } else {
                            vis[k + i][l + j] = true;
                        }
                    }
                }
            }

            if (ok) {
                //cerr << i << " " << j << endl;
                cout << yes << endl;
                return 0;
            }
        }
    }
    cout << no << endl;
    return 0;
}