#include <bits/stdc++.h>

using namespace std;

int h, w;
bool s[50][50];
bool getS(int i, int j) {
	if (i < 0 || i >= h || j < 0 || j >= w) {
		return false;
	}
	else {
		return s[i][j];
	}
}

int main() {
	cin >> h >> w;
	for (int i = 0;i < h;i++) {
		string si;
		cin >> si;
		for (int j = 0;j < w;j++) {
			s[i][j] = (si[j] == '#');
		}
	}

	int ni = -1, nj;
	for (int i = 0;i < h;i++) {
		for (int j = 0;j < w;j++) {
			if (s[i][j]&&ni==-1) {
				ni = i;
				nj = j;
			}
		}
	}
	if (ni == -1) {
		cout << "NO" << endl;
		return 0;
	}

	for (int i = ni;i < h;i++) {
		for (int j = 0;j < w;j++) {
			if (i == ni && j <= nj) {
				continue;
			}
			if (s[i][j]) {
				int di = i - ni;
				int dj = j - nj;
				bool painted[50][50];
				for (int k = 0;k < h;k++) {
					for (int l = 0;l < w;l++) {
						painted[k][l] = false;
					}
				}
				bool b = true;
				for (int k = ni;k < h;k++) {
					for (int l = 0;l < w;l++) {
						if (k == ni && l < nj) {
							continue;
						}
						if (s[k][l] && !painted[k][l]) {
							painted[k][l] = true;
							int nk = k + di;
							int nl = l + dj;
							if (getS(nk, nl) && !painted[nk][nl]) {
								painted[nk][nl] = true;
							}
							else {
								b = false;
							}
						}
						if (!b)
							break;
					}
					if (!b)
						break;
				}
				if (b) {
					cout << "YES" << endl;
					return 0;
				}
			}
		}
	}

	cout << "NO" << endl;

	return 0;
}