#include<iostream>
#include<string>
#include<cstdio>
#include<vector>
#include<cmath>
#include<algorithm>
#include<functional>
#include<iomanip>
#include<queue>
#include<ciso646>
#include<random>
#include<map>
#include<set>
#include<complex>
#include<bitset>
#include<stack>
#include<unordered_map>
#include<utility>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
typedef long double ld;
const ll INF = 1e+14;
typedef pair<int, int> P;
#define stop char nyaa;cin>>nyaa;
#define rep(i,n) for(int i=0;i<n;i++)
#define per(i,n) for(int i=n-1;i>=0;i--)
#define Rep(i,sta,n) for(int i=sta;i<n;i++)
#define rep1(i,n) for(int i=1;i<=n;i++)
#define per1(i,n) for(int i=n;i>=1;i--)
#define Rep1(i,sta,n) for(int i=sta;i<=n;i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
#define fr first
#define sc second

int h, w;
char mp[50][50];

bool used[50][50];
void solve() {
	cin >> h >> w;
	vector<P> v;
	rep(i, h) {
		rep(j, w) {
			cin >> mp[i][j];
			if (mp[i][j] == '#')v.push_back({ i,j });
		}
	}
	if (v.size() <= 1) {
		cout << "NO" << endl; return;
	}
	rep1(i, v.size() - 1) {
		rep(j, h)rep(k, w)used[j][k] = false;
		used[v[0].fr][v[0].sc] = true;
		int dx = v[i].fr - v[0].fr;
		int dy = v[i].sc - v[0].sc;
		used[v[i].fr][v[i].sc] = true;
		bool f = true;
		rep1(j, v.size() - 1) {
			if (used[v[j].fr][v[j].sc])continue;
			int nex = v[j].fr + dx, ney = v[j].sc + dy;
			if (nex < 0 || nex >= h || ney < 0 || ney >= w) {
				f = false; break;
			}
			if (mp[nex][ney] == '#') {
				used[nex][ney] = true;
			}
			else {
				f = false; break;
			}
		}
		if (f) {
			cout << "YES" << endl; return;
		}
	}
	rep1(i, v.size() - 1) {
		rep(j, h)rep(k, w)used[j][k] = false;
		used[v[0].fr][v[0].sc] = true;
		int dx = v[i].fr - v[0].fr;
		int dy = v[i].sc - v[0].sc;
		used[v[i].fr][v[i].sc] = true;
		bool f = true;
		per1(j, v.size() - 1) {
			if (used[v[j].fr][v[j].sc])continue;
			int nex = v[j].fr + dx, ney = v[j].sc + dy;
			if (nex < 0 || nex >= h || ney < 0 || ney >= w) {
				f = false; break;
			}
			if (mp[nex][ney] == '#') {
				used[nex][ney] = true;
			}
			else {
				f = false; break;
			}
		}
		if (f) {
			cout << "YES" << endl; return;
		}
	}

	cout << "NO" << endl;
}
int main() {
	solve();
	//stop
	return 0;
}