#include <bits/stdc++.h>
#define GET_MACRO(a, b, c, NAME, ...) NAME
#define rep(...) GET_MACRO(__VA_ARGS__, rep3, rep2)(__VA_ARGS__)
#define rep2(i, a) rep3 (i, 0, a)
#define rep3(i, a, b) for (int i = (a); i < (b); i++)
#define repr(...) GET_MACRO(__VA_ARGS__, repr3, repr2)(__VA_ARGS__)
#define repr2(i, a) repr3 (i, 0, a)
#define repr3(i, a, b) for (int i = (b) - 1; i >= (a); i--)
#define chmin(a, b) ((b) < a && (a = (b), true))
#define chmax(a, b) (a < (b) && (a = (b), true))
using namespace std;
typedef long long ll;

int H, W;
string S[55];
int color[55][55];

bool check(int di, int dj) {
	rep (i, H) rep (j, W) color[i][j] = 0;
	rep (i, H) rep (j, W) {
		if (S[i][j] != '#') continue;
		if (color[i][j] != 0) continue;
		int ni = i + di;
		int nj = j + dj;
		if (ni < 0 || ni >= H || nj < 0 || nj >= W) return false;
		if (S[ni][nj] == '.') return false;
		if (color[ni][nj] != 0) return false;
		color[i][j] = 1;
		color[ni][nj] = 2;
	}
	rep (i, H) rep (j, W) {
		if (S[i][j] == '#' && color[i][j] == 0) return false;
	}
	return true;
}

int main() {
	cin >> H >> W;
	rep (i, H) cin >> S[i];
	bool all = true;
	rep (i, H) rep (j, W) all &= S[i][j] == '.';
	if (all) {
		cout << "NO" << endl;
		return 0;
	}
	rep (di, H) rep (dj, W) {
		if (di == 0 && dj == 0) continue;
		if (check(di, dj)) {
			cout << "YES" << endl;
			return 0;
		}
	}
	reverse(S, S + H);
	rep (di, H) rep (dj, W) {
		if (di == 0 && dj == 0) continue;
		if (check(di, dj)) {
			cout << "YES" << endl;
			return 0;
		}
	}
	cout << "NO" << endl;
	return 0;
}