#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

int H,W;
vector<string> V;

struct Point {
    Point(){};
    Point( int a, int b ) { x = a; y = b; };
    int x;
    int y;
};

bool isOK( int x, int y ) {
    return x >= 0 && y >= 0 && x < W && y < H;
}

bool func( int dx, int dy ) {
    vector<string> T(H);
    for ( int i = 0; i < H; i++ ) {
        T[i] = V[i];
    }
    for ( int y = 0; y < H; y++ ) {
    for ( int x = 0; x < W; x++ ) {
        if ( T[y][x] == '#' ) {
            if ( isOK(x+dx,y+dy) && T[y+dy][x+dx] == '#' ) {
                T[y+dy][x+dx] = '.';
                continue;
            }
            if ( isOK(x-dx,y-dy) && T[y-dy][x-dx] == '#' ) {
                T[y-dy][x-dx] = '.';
                continue;
            }
            return false;
        }
    }
    }
    return true;

}

int main() {
    
    cin >> H >> W;    
    V.resize(H);
    for ( int i = 0; i < H; i++ ) {
        cin >> V[i];
    }
    vector<Point> P;
    for ( int y = 0; y < H; y++ ) {
    for ( int x = 0; x < W; x++ ) {
        if ( V[y][x] == '#' ) {
            Point p(x,y);
            P.push_back( p );
        }
    }
    }
    bool ans = false;
    for ( int i = 1; i < P.size(); i++ ) {
        if ( func( P[0].x-P[i].x, P[0].y-P[i].y ) ) { ans = true; }
    }

    cout << ( ans ? "YES" : "NO" ) << endl;

    return 0;
}