#include<bits/stdc++.h>
using namespace std;
using ll = long long;
using PAIR = pair<int, int>;
using PAIRLL = pair<ll,ll>;
using vi = vector<int>;
using vll = vector<ll>;
using vvi = vector<vi>;
using vs = vector<string>;
#define rep(i,n) for(int i=0;i<(n);i++)
#define INF 100000000
#define REP(i,n) for(ll i=0;i<ll(n);i++)
#define REPD(i,n) for(ll i=n-1;i>=0;i--)
#define FOR(i,a,b) for(ll i=a;i<=ll(b);i++)
#define FORD(i,a,b) for(ll i=a;i>=ll(b);i--)
#define FORA(i,I) for(const auto& i:I)
//x:コンテナ
#define ALL(x) x.begin(),x.end() 
#define SIZE(x) ll(x.size()) 
//定数
#define INF32 2147483647 //2.147483647×10^{9}:32bit整数のinf
#define INF64 9223372036854775807 //9.223372036854775807×10^{18}:64bit整数のinf
#define MOD 1000000007 //問題による
#define F first
#define S second
//出力(空白区切りで昇順に)
#define coutALL(x) for(auto i=x.begin();i!=--x.end();i++)cout<<*i<<" ";cout<<*--x.end()<<endl
#define coutALLn(x) for(auto i=x.begin();i!=--x.end();i++)cout<<*i<<endl;cout<<*--x.end()<<endl
ll myceil(ll a,ll b){return (a+(b-1))/b;}
ll myfloor(ll a,ll b){return a/b;}

int vector_finder(std::vector<int> vec, int number) {
  auto itr = std::find(vec.begin(), vec.end(), number);
  size_t index = std::distance( vec.begin(), itr );
  if (index != vec.size()) { // 発見できたとき
    return 1;
  }
  else { // 発見できなかったとき
    return 0;
  }
}

vector<ll> vector_find_ll(vector<ll> vec,ll num){
    int N = vec.size();
    vector<ll> match_num;
    rep(i,N){
        if (vec[i] == num){
            match_num.push_back(i);
        }
    }
    return match_num;
}

ll vector_max(vector<ll> vec){
    ll ret = -INF64;
    rep(i,vec.size()){
        ret = max(ret,vec[i]);
    }
    return ret;
}

ll vector_min(vector<ll> vec){
    ll ret = INF64;
    rep(i,vec.size()){
        ret = min(ret,vec[i]);
    }
    return ret;
}

bool is_ok(vector<string> lsHW,int dx,int dy){
    int H,W;
    vector<string> lsHW2 = lsHW;
    H = lsHW2.size();
    W = lsHW2[0].size();
    rep(i,H-dx){
        rep(j,W-dy){
            if (lsHW2[i][j] == '#'){
                lsHW2[i][j] = '.';
                if (lsHW2[i+dx][j+dy] == '.'){
                    return false;
                }
                else{
                    lsHW2[i+dx][j+dy] = '.';
                }
            }
        }
    }
    rep(i,H){
        rep(j,W){
            if (lsHW2[i][j] == '#'){
                return false;
            }
        }
    }
    return true;
}

bool is_ok2(vector<string> lsHW,int dx,int dy){
    int H,W;
    vector<string> lsHW2 = lsHW;
    H = lsHW2.size();
    W = lsHW2[0].size();
    rep(i,H-dx){
        for(int j=dy;j<=W;j++){
            if (lsHW2[i][j] == '#'){
                lsHW2[i][j] = '.';
                if (lsHW2[i+dx][j-dy] == '.'){
                    return false;
                }
                else{
                    lsHW2[i+dx][j-dy] = '.';
                }
            }
        }
    }
    rep(i,H){
        rep(j,W){
            if (lsHW2[i][j] == '#'){
                return false;
            }
        }
    }
    return true;
}


int main(){
    int H,W;
    cin >> H >> W;
    vector<string> lsHW(H);
    rep(i,H) cin >>lsHW[i];
    vector<pair<int,int>> lsp;
    int cnt = 0;
    rep(i,H){
        rep(j,W){
            if (lsHW[i][j] == '#'){
                cnt += 1;
            }
            lsp.push_back({i,j});
        }
    }
    if (cnt == 0){
        cout << "NO" << endl;
        return 0;
    }
    for (const auto & p:lsp){
        if (is_ok(lsHW,p.first,p.second)|is_ok2(lsHW,p.first,p.second)){
            cout << "YES" << endl;
            return 0;
        }
    }
    cout << "NO" << endl;
}