#include<bits/stdc++.h>
using namespace std;

int main(){
    int H, W;
    cin >> H >> W;
    vector<string> A(H);
    for(auto &&s:A)cin >> s;
    for(int my = 0; my <= 50; my++){
        for(int mx = 0; mx <= 50; mx++){
            if(my == 0 && mx == 0)continue;
            bool flag = true;
            vector<vector<bool>> used(H, vector<bool>(W));
            for(int y = 0; y < H; y++){
                for(int x = 0; x < W; x++){
                    if(used[y][x])continue;
                    if(A[y][x] != '#')continue;
                    if(y + my >= H || x + mx >= W){
                        flag = false;
                        continue;
                    }
                    used[y][x] = true;
                    if(A[y + my][x + mx] == '#'){
                        used[y + my][x + mx] = true;
                    }else{
                        flag = false;
                    }
                }
            }
            if(flag){
                cout << "YES" << '\n';
                return 0;
            }
        }
    }
    cout << "NO" << '\n';
}