#include <bits/stdc++.h>
// #include <atcoder/all>
// #include "icld.cpp"
using namespace std;
using ll = long long int;
using vi = vector<int>;
using si = set<int>;
using vll = vector<ll>;
using vvi = vector<vector<int>>;
using ss = string;
using db = double;
template<typename T> using minpq = priority_queue <T,vector<T>,greater<T>>;
const int dx[4] = {1,0,-1,0};
const int dy[4] = {0,1,0,-1};
#define V vector
#define P pair<int,int>
#define PLL pair<ll,ll>
#define rep(i,s,n) for(int i=(s);i<(int)(n);i++)
#define rev(i,s,n) for(int i=(s);i>=(int)(n);i--)
#define reciv(v,n) vll (v)((n)); rep(i,0,(n))cin>>v[i]
#define all(v) v.begin(),v.end()
#define rall(v) v.rbegin(),v.rend()
#define ci(x) cin >> x
#define cii(x) ll x;cin >> x
#define cci(x,y) ll x,y;cin >> x >> y
#define co(x) cout << x << endl
#define pb push_back
#define eb emplace_back
#define rz resize
#define pu push
#define sz(x) int(x.size())
#define vij v[i][j]
// ll p = 1e9+7;
// ll p = 998244353;
// n do -> n*pi/180
#define yn cout<<"Yes"<<endl;else cout<<"No"<<endl
#define YN cout<<"YES"<<endl;else cout<<"NO"<<endl
template<class T>void chmax(T &x,T y){x=max(x,y);}
template<class T>void chmin(T &x,T y){x=min(x,y);}

int main(){
  cci(h,w);
  V<P> v;
  map<P,int> mp;
  int cnt=0;

  rep(i,0,h){
    rep(j,0,w){
      char c;ci(c);
      if(c=='#')v.pb(P(i,j)),mp[P(i,j)]=cnt++;
    }
  }

  int n=sz(v);
  if(n==0 or n%2==1)return co("NO"),0;

  rep(i,1,n){
    int x=v[i].first-v[0].first;
    int y=v[i].second-v[0].second;

    vi bl(n,0);
    bl[0]=bl[i]=1;

    int f=1;
    rep(j,0,n){
      if(bl[j])continue;

      P np=P(v[j].first+x,v[j].second+y);
      if(!mp.count(np)){
        f=0;
        break;
      }

      bl[j]=bl[mp[np]]=1;
    }
  
    if(f)return co("YES"),0;
  }

  co("NO");
}