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

const string msg[] = { "NO", "YES" };

int in_range( int n, int m, int x, int y ){
  return 0 <= x and x < n and 0 <= y and y < m; 
}

int ok( const vector< string > &G, int dx, int dy ){
  vector< string > col( G.size() );
  for( int i = 0; i < G.size(); ++i )
    col[ i ] = G[ i ];
  for( int i = 0; i < col.size(); ++i )
    for( int j = 0; j < col[ i ].size(); ++j )
      if( col[ i ][ j ] == '#' ){
        if( not in_range( col.size(), col[ 0 ].size(), i + dx, j + dy ) ) continue;
        if( col[ i + dx ][ j + dy ] != '#' )
          return 0;
        col[ i ][ j ] = 'X';
        col[ i + dx ][ j + dy ] = 'O';
      }
  for( int i = 0; i < col.size(); ++i )
    for( int j = 0; j < col[ i ].size(); ++j )
      if( col[ i ][ j ] == '#' )
        return 0;
  return 1;
}

signed main(){
  int H, W; cin >> H >> W;
  vector< string > G( H );
  for( int i = 0; i < H; ++i )
    cin >> G[ i ];
  int sharpcnt = 0;
  for( int i = 0; i < H; ++i )
    for( int j = 0; j < W; ++j )
      sharpcnt += G[ i ][ j ] == '#';
  if( sharpcnt == 0 )
    cout << msg[ 0 ] << endl, exit( 0 );
  for( int i = -( H - 1 ); i <= H - 1; ++i )
    for( int j = -( W - 1 ); j <= W - 1; ++j ) if( not ( i == 0 and j == 0 ) )
      if( ok( G, i, j ) )
        cout << msg[ 1 ] << endl, exit( 0 );
  cout << msg[ 0 ] << endl;
  return 0;
}