#include <bits/stdc++.h>
#define ll long long
#define INF 1000000005
#define MOD 1000000007
#define EPS 1e-10
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define each(a, b) for(auto (a): (b))
#define all(v) (v).begin(),(v).end()
#define fi first
#define se second
#define pb push_back
#define show(x) cout <<#x<<" = "<<(x)<<endl
#define spair(p) cout <<#p<<": "<<p.fi<<" "<<p.se<<endl
#define svec(v) cout<<#v<<":";rep(kbrni,v.size())cout<<" "<<v[kbrni];cout<<endl
#define sset(s) cout<<#s<<":";each(kbrni,s)cout <<" "<<kbrni;cout<<endl

using namespace std;

typedef pair<int,int>P;

const int MAX_N = 51;

string s[MAX_N];
string bf[MAX_N];
int h,w;

bool check(string* mp,int u,int v)
{
    rep(i,h){
        rep(j,w){
            if(i + u < h && j + v < w){
                if(mp[i][j] == '.'){
                    if(mp[i+u][j+v] == '#'){
                        return false;
                    }
                }else{
                    if(mp[i+u][j+v] == '#'){
                        mp[i][j] = '.';
                        mp[i+u][j+v] = '.';
                    }else{
                        return false;
                    }
                }
            }else{
                if(mp[i][j] == '#'){
                    return false;
                }
            }
        }
    }
    return true;
}

int main()
{
    cin >> h >> w;
    rep(i,h){
        cin >> s[i];
        bf[i] = s[i];
    }
    rep(i,h){
        rep(j,w){
            if(i != 0 || j != 0){
                rep(k,h){
                    s[k] = bf[k];
                }
                if(check(s,i,j)){
                    cout << "YES\n";
                    return 0;
                }
            }
        }
    }
    cout << "NO\n";
    return 0;
}