#include <bits/stdc++.h>
#define REP(i,n,N) for(int i=(n);i<(int)N;i++)
#define p(s) cout<<(s)<<endl
#define ck(n,a,b) ((a)<=(n)&&(n)<(b))
using namespace std;

int main(){
	int H,W;
	cin>>H>>W;
	string s[51];
	REP(i,0,H) cin>>s[i];
	string ans="NO";
	REP(dy,-H+1,H){
		REP(dx,-W+1,W){
			if(dy==0&&dx==0) continue;
			string tmps[51];
			REP(i,0,H) tmps[i]=s[i];
			bool flag=true;
			REP(i,0,H){
				REP(j,0,W){
					if(tmps[i][j]=='.') continue;
					int nx=j+dx;
					int ny=i+dy;
					if(!ck(ny,0,H)||!ck(nx,0,W)) {
						flag=false;
						break;
					}
					if(tmps[ny][nx]=='#'){//can move
						tmps[ny][nx]='.';//used
					}else{
						flag=false;
						break;
					}
				}
				if(!flag) break;
			}
			if(flag) {
				ans="YES";
			}
		}
	}
	p(ans);
	return 0;
}