module main;
// https://yukicoder.me/submissions/18400 より
// 2次元グリッド
import std;

void main()
{
	// 入力
	int H, W;
	readln.chomp.formattedRead("%d %d", H, W);
	auto S = new string[](H);
	foreach (ref s; S)
		s = readln.chomp;
	// 答えの計算と出力
	foreach (i; 0 .. H + 1) {
		foreach (j; -W .. W + 1) {
			if (i == 0 && j == 0) continue;
			auto check = new bool[][](H, W);
			bool ok = true;
			int count = 0;
			foreach (k; 0 .. H) {
				foreach (l; 0 .. W) {
					if (S[k][l] == '.' || check[k][l]) continue;
					count++;
					check[k][l] = true;
					int nk = k + i, nl = l + j;
					if (nk < 0 || H <= nk || nl < 0 || W <= nl) {
						ok = false;
						break;
					}
					if (S[nk][nl] == '#' && !check[nk][nl]) {
						check[nk][nl] = true;
					} else {
						ok = false;
						break;
					}
				}
			}
			if (count == 0) ok = false;
			if (ok) {
				writeln("YES");
				return;
			}
		}
	}
	writeln("NO");
}