#define _USE_MATH_DEFINES
#include<stdio.h>
#include<string>
#include<iostream>
#include<cctype>
#include<cstdio>
#include<vector>
#include<stack>
#include<queue>
#include <algorithm>
#include<math.h>
#include<set>
#include<map>
#include<iomanip>

//#include<bits/stdc++.h>


using namespace std;


int main() {
	
	int h, w; cin >> h >> w;
	bool n[550][550] = {};
	string p;
	int r = 0;
	for (int i = 0; i < h; i++) {

		cin >> p;
		for (int j = 0; j < p.size(); j++) {
			if (p[j] == '#') {
				n[i][j] = 1;
				r++;
			}
		}
	//	cout << i;
	}
	//cout << r << endl;
	if (r % 2||r==0) {
		cout << "NO" << endl; return 0;
	}
	bool R = 0;
	for (int i = 0; i < h; i++) {
		
		for (int j = 0; j < w; j++) {
			if (!i && !j)continue;
			bool f[550][550] = {}; bool p = 0;
				int y = 0;//cout << i;
			for (int I = 0; I < h; I++) {

				
				for (int J = 0; J < w; J++) {
				//	cout << n[I][J]<< n[I+i][J+j];
					if (n[I][J] && n[I + i][J + j]) {
						if (f[I][J]==0&&f[I + i][J + j] == 0) {
							y += 2;
							f[I][J] = 1;
							f[I+i][J+j] = 1;
						}
						else if(!f[I][J]&& f[I + i][J + j])  p= 1;
					}
					if (p)break;
				}
				//cout << y << i << j << endl;;
				if (!p&&y == r) {
					cout << "YES" << endl;
					return 0;
				}
			}

			

		}
		
	}
	cout << "NO" << endl;
	return 0;

}