#include<iostream>
using namespace std;

int h, w;
char c[50][50];
char original[50][50];

bool search(int y, int x) {
	for (int i = 0; i < h; i++) {
		for (int j = 0; j < w; j++) {
			if (c[i][j] == '#') {
				if (i + y >= h || j + x >= w || j + x < 0 || c[i + y][j + x] != '#') {
					return false;
				}
				else {
					c[i][j] = '.';
					c[i + y][j + x] = '.';
				}
			}
		}
	}
	return true;
}

void reset() {
	for (int i = 0; i < h; i++) {
		for (int j = 0; j < w; j++) {
			c[i][j] = original[i][j];
		}
	}
}

int main() {
	int count = 0;
	cin >> h >> w;
	for (int i = 0; i<h; i++) {
		for (int j = 0; j<w; j++) {
			cin >> original[i][j];
			if (original[i][j] == '#')count++;
		}
	}
	if (count == 0) {
		cout << "NO" << endl;
		return 0;
	}
	reset();
	for (int y = 0; y<h; y++) {
		for (int x = 1 - w; x < w; x++) {
			if (x == 0 && y == 0)continue;
			if (search(y, x)) {
				cout << "YES" << endl;
				return 0;
			}
			reset();
		}
	}
	cout << "NO" << endl;
	return 0;
}