#include <iostream>
#include <queue>
#include <vector>
#include <limits>
using namespace std;

int main()
{
	int H, W;
	string s[55];
	cin >> H >> W;
	int cnt = 0;

	for (int i = 0; i < H; ++i) cin >> s[i];
	for (int i = 0; i < H; ++i)
		for (int j = 0; j < W; ++j)
			cnt += s[i][j] == '#';

	if (cnt & 1 || cnt == 0) {
		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;
			int match = 0;
			vector<vector<bool>> used(H + 1, vector<bool>(W + 1, false));
			for (int k = 0; k < H && k + i < H; ++k)
				for (int l = 0; l < W && l + j < W; ++l) {
					if (k + i < 0 || l + j < 0) continue;
					if (s[k][l] == '#' && s[k + i][l + j] == '#') {
						if (!used[k][l] && !used[k + i][l + j]) {
							++match;
							used[k][l] = used[k + i][l + j] = true;
						}
					}
				}
			if (match == cnt / 2) {
				cout << "YES" << endl;
				return 0;
			}
		}
	}
	cout << "NO" << endl;

	return 0;
}