#include "bits/stdc++.h"
using namespace std;
#define FOR(i,j,k) for(int (i)=(j);(i)<(int)(k);++(i))
#define rep(i,j) FOR(i,0,j)
#define each(x,y) for(auto &(x):(y))
#define mp make_pair
#define mt make_tuple
#define all(x) (x).begin(),(x).end()
#define debug(x) cout<<#x<<": "<<(x)<<endl
#define smax(x,y) (x)=max((x),(y))
#define smin(x,y) (x)=min((x),(y))
#define MEM(x,y) memset((x),(y),sizeof (x))
#define sz(x) (int)(x).size()
#define pb push_back
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<ll> vll;

int H, W, c[50][50];
string S[50];

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    cin >> H >> W;
    rep(y, H)cin >> S[y];

    FOR(dy, -H + 1, H)FOR(dx, -W + 1, W) if (dy != 0 || dx != 0) {
        MEM(c, 0);
        
        bool ok = [&] {
            rep(y, H)rep(x, W) if (S[y][x] == '#' && !c[y][x]) {
                c[y][x] = 1;
                int ny = y + dy, nx = x + dx;
                if (ny >= H || nx >= W || ny < 0 || nx < 0 || S[ny][nx] != '#' || c[ny][nx]) {
                    return false;
                }
                c[ny][nx] = 1;
            }
            return true;
        }();
        if (ok) {
            cout << "YES" << endl;
            return 0;
        }
    }
    cout << "NO" << endl;
}