#include "bits/stdc++.h"
using namespace std;
#define ll long long int
#define rep(i,n) for( int i = 0; i < n; i++ )
#define rrep(i,n) for( int i = n; i >= 0; i-- )
#define REP(i,s,t) for( int i = s; i <= t; i++ )
#define RREP(i,s,t) for( int i = s; i >= t; i-- )
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define INF 2000000000
#define mod 1000000007
#define INF2 1000000000000000000


int main(void)
{
	cin.tie(0);
	ios::sync_with_stdio(false);
	int H, W;
	cin >> H >> W;
	char s[H][W];
	rep(i, H) rep(j, W) cin >> s[i][j];
	rep(l, H) {
		rep(r, W) {
			if (l == 0 && r == 0) continue;
			char k[H][W];
			rep(i, H) rep(j, W) k[i][j] = s[i][j];
			bool f = true;
			rep(i, H - l) {
				if (f == false) break;
				rep(j, W - r) {
					//cout << i + l << " " << j + r << endl;
					if (k[i][j] == '#') {
						if (k[i + l][j + r] != '#') {
							f = false;
							break;
						}
						k[i][j] = '.';
						k[i + l][j + r] = '.';
					}
				}
			}
			rep(i, H) {
				rep(j, W) {
					if (k[i][j] == '#') {
						f = false;
						break;
					}
				}
			}
			if (f) {
				cout << "YES" << endl;
				return 0;
			}
		}
	}
	cout << "NO" << endl;

	return 0;
}