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

char c[105][105];
int a[105][105];
int b[105][105];

int main(){
  int h, w; cin >> h >> w;
  for(int i = 0; i < h; i++){
    for(int j = 0; j < w; j++){
      cin >> c[i][j];
      if(c[i][j]=='#') a[i][j] = 1;
      else a[i][j] = -1;
    }
  }
  for(int i = 0; i < h; i++){
    for(int j = 0; j < w; j++){
      if(i==0&&j==0)continue;
      for(int k = 0; k < 2*h; k++){
        for(int l = 0; l < 2*w; l++){
          b[k][l] = a[k][l];
        }
      }
      for(int k = 0; k < h; k++){
        for(int l = 0; l < w; l++){
          if(a[k][l]==1)b[k+i][l+j] += a[k][l];
        }
      }
      bool flag = true;
      for(int k = 0; k < h; k++){
        for(int l = 0; l < w; l++){
          if(b[k][l]==1){
            if(b[k+i][l+j]!=2) flag = false;
          }
          if(b[k][l]==2){
            if(b[k-i][l-j]!=1) flag = false;
          }
        }
      }
      if(flag){
        cout << "YES" << endl;
        return 0;
      }
    }
  }
  cout << "NO" << endl;        
  return 0;
}