#include <bits/stdc++.h>
using namespace std;
using ll=long long;

#define itn long long
#define rep(i,n) for(int i=0;i<(int)n;++i)
#define rrep(i,n) for(int i=(int)(n);i>=0;--i)
#define debug(x) cout << #x << "=" << (x) << endl;
const ll MOD=1e9+7;

template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return true;}return false;}
template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return true;}return false;}
template<typename T> void fail(T v){cout << v << endl;exit(0);}
//template end

void solve(){
  int H,W;
  cin>>H>>W;
  vector<string> grid(H);
  rep(i,H)
    cin>>grid[i];
  int ct=0;
  rep(i,H)
    rep(j,W)
      if(grid[i][j]=='#')ct++;
  if(ct%2)fail("NO");
  ct>>=1;
  
  for(int i=0;i<H;i++)
    for(int j=0;j<W;j++){
      int c=0;
      vector<vector<bool>> use(51,vector<bool>(51));
      if(!(i|j))continue;
      rep(y,H-i)
        rep(x,W-j)
          if(!use[y][x]&&grid[y][x]=='#'&&grid[y+i][x+j]=='#')
            {c++;use[i+y][x+j]=true;}
      //debug(i);debug(j);debug(c);
      //cout<<endl;
      if(c==ct)fail("YES");
    }
    cout<<"NO"<<endl;
}
 
int main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(20);
  solve();
  return 0;
}