#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <string>
#include <vector>

#define repf(x,fr,to) for(int (x)=(fr);(x)<(to);(x)++)
#define rep(x,to) for(int (x)=0;(x)<(to);(x)++)
#define sz(v) (int)(v).size()

using namespace std;

int main()
{
	
	int h,w;
	cin >> h>>w;
	vector<string> s(h);
	rep(i,h) cin >> s[i];

	vector<int> gy, gx;
	rep(i,h) rep(j,w) if(s[i][j]=='#') gy.push_back(i), gx.push_back(j);
	if(sz(gy) <2 || sz(gy) %2 ){ puts("NO");exit(0);}
	
	repf(i,1,sz(gy)){
		int dy=gy[i]-gy[0], dx=gx[i]-gx[0];
		auto ump = s;
		rep(j, sz(gy)){
			if(ump[gy[j]][gx[j]] !='#') continue;
			int ny= gy[j] + dy, nx = gx[j] + dx;
			if(ny<0 || ny>=h || nx<0 || nx>=w) goto lpend;
			if(ump[ny][nx] =='#') ump[gy[j]][gx[j]] = ump[ny][nx] = 'A';
		}
		rep(i,h) rep(j,w) if(ump[i][j]=='#') goto lpend;
		puts("YES"); exit(0);
		lpend: ;
	}
	puts("NO");

	return 0;
}