#include <bits/stdc++.h>

using namespace std;
using ll = long long;
template <typename T>
using min_priority_queue = priority_queue<T, vector<T>, greater<T>>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
using Graph = vector<vector<int>>;

const ll INF = 1LL << 60;

template <class T>
void chmax(T& a, T b) {
    if (b > a) a = b;
}
template <class T>
void chmin(T& a, T b) {
    if (b < a) a = b;
}

template <typename T, typename S>
std::ostream& operator<<(std::ostream& os, const pair<T, S>& x) noexcept {
    return os << "(" << x.first << ", " << x.second << ")";
}

template <typename T>
void print_vector(vector<T> a) {
    cout << '[';
    for (int i = 0; i < a.size(); i++) {
        cout << a[i];
        if (i != a.size() - 1) {
            cout << ", ";
        }
    }
    cout << ']' << endl;
}

template <typename T>
vector<T> s2v(set<T>& s) {
    vector<T> vec;
    for (auto& v : s) {
        vec.push_back(v);
    }
    return vec;
}

bool is_ok(int i0, int j0, vector<vector<char>>& Mat) {
    ll H = Mat.size();
    ll W = Mat[0].size();
    set<pll> reds, blues;
    for (int i = H - 1; i >= 0; i--) {
        for (int j = W - 1; j >= 0; j--) {
            if (Mat[i][j] == '#') {
                if (i >= i0 && j >= j0) {
                    if (blues.count({i, j})) {
                        reds.insert({i, j});
                    } else {
                        blues.insert({i - i0, j - j0});
                    }
                } else {
                    reds.insert({i, j});
                }
            }
        }
    }
    if (reds.size() != blues.size()) {
        return false;
    }
    auto reds_vec = s2v(reds);
    auto blues_vec = s2v(blues);
    ll N = reds.size();
    sort(reds_vec.begin(), reds_vec.end());
    sort(blues_vec.begin(), blues_vec.end());
    for (int i = 0; i < N; i++) {
        if (reds_vec[i].first != blues_vec[i].first) return false;
        if (reds_vec[i].second != blues_vec[i].second) return false;
    }
    return true;
}

int main() {
    ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    ll H, W;
    cin >> H >> W;
    vector<vector<char>> Mat(H, vector<char>(W, 0));
    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) {
            cin >> Mat[i][j];
        }
    }
    for (int i = 0; i < H; i++) {
        for (int j = 0; j < W; j++) {
            if (i == 0 && j == 0) continue;
            if (is_ok(i, j, Mat)) {
                std::cout << "YES"
                          << "\n";
                return 0;
            }
        }
    }
    std::cout << "NO"
              << "\n";
    return 0;
}