#include <iostream>
using namespace std;

bool inside(int a, int b, int alim, int blim){
	return 0 <= a && a < alim && 0 <= b && b < blim;
}

int main(){
	int h, w;
	cin >> h >> w;
	string s[h];
	for(int i = 0; i < h; i++) cin >> s[i];
	{
		bool f = true;
		for(int i = 0; i < h; i++) for(auto& c:s[i]) f &= c == '.';
		if(f){
			cout << "NO" << endl;
			return 0;
		}
	}
	for(int mh = -h; mh <= h; mh++) for(int mw = -w; mw <= w; mw++){
		if(mh == 0 && mw == 0) continue;
		bool f = true, done[h][w]{};
		for(int i = 0; i < h; i++) for(int j = 0; j < w; j++) if(s[i][j] == '#' && !done[i][j]){
			if(!inside(i + mh, j + mw, h, w)) goto next;
			if(s[i + mh][j + mw] != '#' || done[i + mh][j + mw]) goto next;
			done[i][j] = done[i + mh][j + mw] = true;
		}
		for(int i = 0; i < h; i++) for(int j = 0; j < w; j++) if(s[i][j] == '#') f &= done[i][j];
		if(f){
			cout << "YES" << endl;
			return 0;
		}
		next:;
	}
	cout << "NO" << endl;
}