#include <iostream>
#include <algorithm>
#include <vector>
#include <string>

void solve() {
    int h, w;
    std::cin >> h >> w;

    std::vector<std::string> ss(h);
    for (auto& s : ss) std::cin >> s;

    for (int q = 0; q < 2; ++q) {
        for (int dx = 0; dx < h; ++dx) {
            for (int dy = 0; dy < w; ++dy) {
                auto ts = ss;
                bool judge = true;

                for (int x = 0; x < h; ++x) {
                    for (int y = 0; y < w; ++y) {
                        if (ts[x][y] != '#') continue;
                        ts[x][y] = 'O';

                        int nx = x + dx,
                            ny = y + dy;

                        if (nx >= h || ny >= w ||
                            ts[nx][ny] != '#') {
                            judge = false;

                        } else {
                            ts[nx][ny] = 'X';
                        }
                    }
                }

                if (judge) {
                    if (q) std::reverse(ts.begin(), ts.end());
                    for (auto& t : ts) std::cerr << t << std::endl;

                    std::cout << (dx == 0 && dy == 0 ? "NO" : "YES")
                              << std::endl;
                    return;
                }
            }
        }

        std::reverse(ss.begin(), ss.end());
    }

    std::cout << "NO" << std::endl;
}

int main() {
    std::cin.tie(nullptr);
    std::ios::sync_with_stdio(false);

    solve();

    return 0;
}