#include <iostream>

#include <vector>
#include <map>
#include <algorithm>
#include <fstream>
#include<cstdio>
#include<iomanip>
#include<stack>
#include<queue>
#include<string>
#include <cstdlib>
#include <typeinfo>

#define REP(i, n) for(int i=0;i<n;i++)
#define REP2(i, s, n) for(int i=s;i<n;i++)
#define REP_1(i, n) for(int i=1;i<n+1;i++)
#define bitSearch(bit, n) for(int bit = 0; bit < (1 << n); bit++)
using namespace std;

template<class T>
void print(const T &value) {
    std::cout << value << std::endl;
}

void yesno(bool a) { if (a)cout << "yes" << endl; else cout << "no" << endl; }

void YesNo(bool a) { if (a)cout << "Yes" << endl; else cout << "No" << endl; }

void YESNO(bool a) { if (a)cout << "YES" << endl; else cout << "NO" << endl; }

typedef long long ll;
typedef unsigned long ul;
typedef long double ld;

template<class T>
inline bool chmin(T &a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}

template<class T>
inline bool chmax(T &a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}

ll INF = 10000000;
ll mod = 1000000007;//10^9+7
//int dx[8] = {-1, 0, 0, 1, -1, -1, 1, 1};
//int dy[8] = {0, -1, 1, 0, -1, 1, -1, 1};
using Graph = vector<vector<int>>;//隣接リスト:G[i]にはiと隣接する頂点が入るよ。
using P = pair<int, int>;//BFSで利用。queueに入れる。
using PP = pair<int, P>; //dijkstraで利用,priority_queueに入れる。
using p_queue = priority_queue<int, vector<int>, greater<int>()>;
//struct edge{int to, cost};



//番号ズレ注意！！
int main() {
    int H, W;
    cin >> H >> W;
    string S[H];
    vector<P> black;
    REP(i, H) {
        cin >> S[i];
        REP(j, W) {
            if (S[i][j] == '#') { black.emplace_back(i, j); }
        }
    }
    bool two = false;
    int N = black.size();
    REP_1(i, N - 1) {//black[0]がblack[i]に映るような平行移動を考える。
        int color[H][W];//color[i][j]:=-1なら未確定，0ならred,1ならblue;
        REP(k, H) { REP(j, W) { color[k][j] = -1; }}
        color[black[0].first][black[0].second] = color[black[i].first][black[i].second] = 1;
        int dx = black[i].first - black[0].first;
        int dy = black[i].second - black[0].second;
        bool can = true;
        int j = 1;
        while (j < N) {
            if (color[black[j].first][black[j].second] != -1) { j++;continue; }
            color[black[j].first][black[j].second] = 0;
            int nx = black[j].first + dx;
            int ny = black[j].second + dy;
            if (nx < 0 || nx >= H || ny < 0 || ny >= W) {
                can = false;
                break;
            }
            if (S[nx][ny] == '.') {
                can = false;
                break;
            }
            if (color[nx][ny] == 0) {
                can = false;
                break;
            }
            color[nx][ny] = 1;
            j++;
        }
        if (can) {
            two = true;
            break;
        } else {
            continue;
        }
    }
    YESNO(two);
}