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

//重み付きUnion_Find(和)
struct Weighted_dsu {
  public:
    Weighted_dsu() : _n(0) {}
    Weighted_dsu(int n) : _n(n), parent_or_size(n, -1),diff_weight(n,0) {}

    bool merge(int a, int b, long long w) {
        int x = leader(a), y = leader(b);
        if(x==y){
            if(diff(a,b)==w)return true;
            return false;
        }
        w += diff_weight[a]; w -= diff_weight[b];
        if (-parent_or_size[x] < -parent_or_size[y]) std::swap(x, y),w*=-1;
        parent_or_size[x] += parent_or_size[y];
        parent_or_size[y] = x;
        diff_weight[y] = w;
        return true;
    }
    long long diff(int x, int y) {
        leader(x),leader(y);
        return diff_weight[y] - diff_weight[x];
    }
    bool same(int a, int b) {
        return leader(a) == leader(b);
    }
    int leader(int a) {
        if (parent_or_size[a] < 0) return a;
        int r = leader(parent_or_size[a]);
        diff_weight[a] += diff_weight[parent_or_size[a]];
        return parent_or_size[a] = r;
    }
    int size(int a) {
        return -parent_or_size[leader(a)];
    }
    std::vector<std::vector<int>> groups() {
        std::vector<int> leader_buf(_n), group_size(_n);
        for (int i = 0; i < _n; i++) {
            leader_buf[i] = leader(i);
            group_size[leader_buf[i]]++;
        }
        std::vector<std::vector<int>> result(_n);
        for (int i = 0; i < _n; i++) {
            result[i].reserve(group_size[i]);
        }
        for (int i = 0; i < _n; i++) {
            result[leader_buf[i]].push_back(i);
        }
        result.erase(
            std::remove_if(result.begin(), result.end(),
                           [&](const std::vector<int>& v) { return v.empty(); }),
            result.end());
        return result;
    }
    private:
        int _n;
        std::vector<int> parent_or_size;
        std::vector<long long> diff_weight;
};

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;
            Weighted_dsu uf(H * W);
            for(int y = 0; y < H; y++){
                for(int x = 0; x < W; x++){
                    if(A[y][x] == '#' && uf.size(y * W + x) == 1){
                        if(y + my >= H || x + mx >= W){
                            flag = false;
                            continue;
                        }
                        if(A[y + my][x + mx] == '#'){
                            uf.merge(y * W + x, (y + my) * W + x + mx, 1);
                        }else{
                            flag = false;
                        }
                    }
                }
            }
            if(flag){
                cout << "YES" << '\n';
                return 0;
            }
        }
    }
    cout << "NO" << '\n';
}