#include <bits/stdc++.h>

#define rep(i, n) for (int (i) = 0; (i) < (int)(n); (i)++)

using namespace std;
typedef long long ll;

const int MAXH = 64;
string s[MAXH];
bool used[MAXH][MAXH];
int H, W;

bool ok(int dx, int dy) {
    memset(used, 0, sizeof(used));
    for (int y = 0; y < H; y++) {
        for (int x = 0; x < W; x++) {
            if (s[y][x] == '.' || used[y][x]) continue;
            used[y][x] = true;
            int ny = y+dy, nx = x+dx;
            if (ny < 0 || ny >= H || nx < 0 || nx >= W) return false;
            if (s[ny][nx] == '#' && !used[ny][nx]) {
                used[ny][nx] = true;
                continue;
            } else {
                return false;
            }
        }
    }
    for (int y = 0; y < H; y++) for (int x = 0; x < W; x++) {
        if (s[y][x] == '#' && !used[y][x]) return false;
    }
    return true;
}

int main() {
    cin >> H >> W;
    for (int i = 0; i < H; i++) {
        cin >> s[i];
    }
    for (int dx = -W; dx <= W; dx++) {
        for (int dy = -H; dy <= H; dy++) {
            if (ok(dx, dy)) {
                cout << "YES" << endl;
                return 0;
            }
        }
    }
    cout << "NO" << endl;
    return 0;
}