#include <bits/stdc++.h>

using namespace std;

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);
	int H, W;
	cin >> H >> W;
	vector<string> s(H);
	bool ans = false;
	for (int i = 0; i < H; i++) cin >> s[i];
	int count = 0;
	for (int i = 0; i < H; i++) {
		for (int j = 0; j < W; j++) {
			count += (s[i][j] == '#');
		}
	}

	if (count == 0) {
		cout << "NO" << endl;
		return 0;
	}

	for (int dh = -H; dh <= H; dh++) {
		for (int dw = -W; dw <= W; dw++) {
			if (dh == 0 && dw == 0) continue;
			bool flag = true;
			vector< vector<bool> > memo(H, vector<bool>(W, false));
			for (int h = 0; h < H; h++) {
				for (int w = 0; w < W; w++) {
					if (s[h][w] == '.' || memo[h][w]) continue;
					memo[h][w] = true;
					int nh = h + dh;
					int nw = w + dw;
					if (nh < 0 || nh >= H || nw < 0 || nw >= W) {
						flag = false;
						break;
					}
					if (s[nh][nw] == '.' || memo[nh][nw]) {
						flag = false;
						break;
					}
					memo[nh][nw] = true;
				}
				if (!flag) break;
			}
			if (flag) {
				ans = true;
				break;
			}
		}
		if (ans) break;
	}
	cout << (ans ? "YES" : "NO") << endl;
	return 0;
}