#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
#include <functional>
#include <cmath>
#include <iomanip>
#include <stack>
#include <queue>
#include <numeric>
#include <map>
#include <unordered_map>
#include <set>
#include <fstream>
#include <chrono>
#include <random>
#include <bitset>
#define rep(i,n) for(int i=0;i<(n);i++)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define sz(x) ((int)(x).size())
#define pb push_back
#define mod 1000000007
using ll = long long;
using namespace std;
ll gcd(ll a, ll b) {return b?gcd(b,a%b):a;}
ll lcm(ll a, ll b) {return a/gcd(a,b)*b;}

int main(){
  int H,W; cin >> H >> W;
  vector<string> S(H); rep(i,H) cin >> S[i];
  int blk = 0;
  rep(y,H) rep(x,W) if(S[y][x]=='#') blk++;
  if(blk == 0 || blk %2 == 1) {
    cout << "NO" << endl;
    return 0;
  }
  for(int dx = -50; dx <= 50; dx++){
    for(int dy = -50; dy <= 50; dy++){
      vector<string> tmp = S;
      int cnt = 0;
      rep(y,H){
        rep(x,W){
          if(tmp[y][x] == '#'){
            if(!(0<=y+dy && y+dy<H && 0<=x+dx && x+dx<W)) continue;
            if(tmp[y+dy][x+dx] == '#'){
              cnt++;
              tmp[y][x] = tmp[y+dy][x+dx] = '.';
            }
            else{
              x=y=100000; break;
            }
          }
        }
        if(y==H-1 && cnt*2==blk){
          cout << "YES" << endl;
          return 0;
        }
      }
    }
  }

  cout << "NO" << endl;
  return 0;
}