#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;

static const double EPS = 1e-8;
static const double PI = 4.0 * atan(1.0);
static const double PI2 = 8.0 * atan(1.0);

#define REP(i,n)	for(int i=0;i<(int)n;++i)
#define ALL(c)		(c).begin(),(c).end()
#define CLEAR(v)	memset(v,0,sizeof(v))
#define MP(a,b)		make_pair((a),(b))
#define ABS(a)		((a)>0?(a):-(a))
#define FOR(i,s,n)	for(int i=s;i<(int)n;++i)

#define YES "YES"
#define NO "NO"

int H, W;
char C[50][50];

int main(int argc, char **argv) {
	cin >> H >> W;
	REP(y, H) REP(x, W) cin >> C[x][y];
	int cnt = 0;
	REP(x, W) REP(y, H) if (C[x][y] == '#') ++cnt;
	if (cnt == 0 || cnt % 2 != 0) {
		cout << NO << endl;
		return 0;
	}
	FOR(dx, -W + 1, W) FOR(dy, -H + 1, H) {
		if (dx == 0 && dy == 0) continue;
		set<int> used;
		bool f = true;
		REP(x, W) {
			REP(y, H) {
				if (C[x][y] == '#' && used.count(y * W + x) == 0) {
					if (x + dx < 0 || y + dy < 0 || x + dx >= W || y + dy >= H || C[x + dx][y + dy] != '#') {
						f = false;
						break;
					}
					used.insert((y + dy) * W + x + dx);
				}
			}
			if (!f) break;
		}
		if (f && used.size() * 2 == cnt) {
			cout << YES << endl;
			return 0;
		}
	}
	cout << NO << endl;
	return 0;
}