#include <bits/stdc++.h>
using namespace std;

int main() {
    int H, W;
    string S[60];
    cin >> H >> W;
    for (int i = 0; i < H; i++) {
        cin >> S[i];
    }

    bool flag = false;
    for (int i = 0; i < H; i++) {
        for (auto& c : S[i])
            if (c == '#')
                flag = true;
    }
    if (!flag) {
        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 flag = true;
            bool seen[60][60] = {};
            for (int x = 0; x < H; x++) {
                for (int y = 0; y < W; y++) {
                    if (x + i >= 0 && x + i < H && y + j >= 0 && y + j < W && !seen[x][y] && !seen[x + i][y + j] && S[x][y] == '#') {
                        seen[x][y] = 1;
                        seen[x + i][y + j] = 1;
                        if (S[x + i][y + j] != '#')
                            flag = false;
                    }
                }
            }
            for (int x = 0; x < H; x++) {
                for (int y = 0; y < W; y++) {
                    if (S[x][y] == '#' && !seen[x][y])
                        flag = false;
                }
            }
            if (flag) {
                cout << "YES" << endl;
                return 0;
            }
        }
    }
    cout << "NO" << endl;
    return 0;
}