#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf 2000000000

int main(){	
	
	int h,w;
	cin>>h>>w;
	
	vector<string> s(h);
	rep(i,h)cin>>s[i];
	
	rep(i,h){
		rep(j,w){
			if(i==0&&j==0)continue;
			
			auto ss = s;
			bool f = true;
			rep(k,h){
				rep(l,w){
					if(ss[k][l]=='#'){
						if(k+i<h&&j+l<w && ss[k+i][j+l]=='#'){
							ss[k+i][j+l] = '.';
						}
						else{
							f = false;
						}
					}
				}
			}
			if(f){
				cout<<"YES"<<endl;
				return 0;
			}
			
		}
	}
	cout<<"NO"<<endl;
	
	return 0;
	
}