#include "bits/stdc++.h"
#include<unordered_map>
#pragma warning(disable:4996)
using namespace std;
using ld = long double;
template<class T>
using Table = vector<vector<T>>;

int main() {
	int H, W; cin >> H >> W;
	vector<vector<int>>field(H,vector<int>(W));
	int num = 0;
	for (int i = 0; i < H; ++i){
		string st; cin >> st;
		for (int j = 0; j < st.size(); ++j){
			if (st[j] == '#'){
				field[i][j] = 1; num++;
			}
			else field[i][j] = 0;
		}
	}
	string st = "NO";
	for (int dx = 0; dx < W; ++dx){
		for (int dy = 0; dy < H; ++dy){
			if (!dx&&!dy)continue;
			vector<vector<int>>used(field);
			int rest = num;
			bool ok = true;
			for (int x = 0; x < W - dx; ++x){
				for (int y = 0; y < H - dy; ++y){
					if (used[y][x]){
						if (used[y + dy][x + dx]){
							used[y][x] = 0;
							used[y + dy][x + dx] = 0;
							rest-=2;
						}
						else{
							ok = false;
							break;
						}
					}
				}
			}
			if (ok&&!rest){
				st = "YES";
				break;
			}
		}
	}
	cout << st << endl;
	return 0;
}