#include<iostream>
using namespace std;
const int BUF = 55;


int row, col;
char b[BUF][BUF];

void read() {
    cin >> row >> col;
    for (int i = 0; i < row; ++i)
        for (int j = 0; j < col; ++j)
            cin >> b[i][j];
}


void work() {
    bool exist = false;
    for (int i = 0; i < row; ++i)
        for (int j = 0; j < col; ++j)
            if (b[i][j] == '#')
                exist = true;
    if (!exist) {
        cout << "NO" << endl;
        return;
    }

    for (int dr = 0; dr < row; ++dr) 
        for (int dc = 0; dc < col; ++dc) {
            if (dr == 0 && dc == 0)
                continue;
            
            bool used[BUF][BUF] = {};
            
            for (int r = 0; r < row; ++r) {
                for (int c = 0; c < col; ++c) {
                    if (b[r][c] == '#' && !used[r][c]) {
                        if (r + dr < row && c + dc < col && b[r + dr][c + dc] == '#') {
                            used[r][c] = used[r + dr][c + dc] = true;
                        }
                        else {
                            goto _fail;
                        }
                    }
                }
            }
            
            cout << "YES" << endl;
            return;
            
        _fail:;
        }
    cout << "NO" << endl;
}


int main() {
    read();
    work();
    return 0;
}