#include <stdio.h>
#include <stdbool.h>
#define rep(i, n) for (i = 0; i < n; i++)

int main() {
	int i, j, k, l;
	int h, w;
	scanf("%d %d", &h, &w);
	getchar();

	bool s[50][50], f[50][50], f2 = false;
	rep(i, h) {
		rep(j, w) {
			s[i][j] = f[i][j] = (getchar() == '#' ? true : false);
			if (!f2 && s[i][j]) f2 = true;
		}
		getchar();
	}
	if (!f2) {
		puts("NO");
		return 0;
	}

	int dy, dx;
	rep(dy, h) rep(dx, w) {
		if (dy == 0 && dx == 0) continue;
		f2 = true;
		rep(i, h) rep(j, w) {
			if (!f[i][j]) continue;
			int y = i + dy, x = j + dx;
			if (!(0 <= y && y <= h && 0 <= x && x <= w) || !f[y][x]) {
				rep(k, h) rep(l, w) f[k][l] = s[k][l];
				f2 = false;
				break;
			}
			else f[i][j] = f[i + dy][j + dx] = false;
		}
		if (f2) {
			puts("YES");
			return 0;
		}
	}
	puts("NO");
	return 0;
}