#include <bits/stdc++.h>
using namespace std;
using ll = long long;
int main() {
	int H, W;
	cin >> H >> W;
	vector<string> S(H);
	for(int i = 0; i < H; i++) cin >> S[i];
	for(int dh = 0; dh < H; dh++) for(int dw = 0; dw < W; dw++) if(dh != 0 || dw != 0) {
		vector<vector<int>> seen(H, vector<int>(W));
		bool f = true;
		for(int i = 0; i < H; i++) for(int j = 0; j < W; j++) if(seen[i][j] == 0 && S[i][j] == '#') {
			seen[i][j] = 1;
			int ni = i + dh, nj = j + dw;
			if(ni < 0 || nj < 0 || ni >= H || nj >= W || (seen[ni][nj] != 0 && seen[ni][nj] != 2) || S[ni][nj] != '#') {
				f = false;
				break;
			}
			seen[ni][nj] = 2;
		}
		for(int i = 0; i < H; i++) for(int j = 0; j < W; j++) if(S[i][j] == '#') {
			if(seen[i][j] == 0) f = false;
		}
		if(f) {
			cout << "YES\n";
			return 0;
		}
	}
	cout << "NO\n";
}