#include <string>
#include <vector>
#include<iostream>
#include<cstdio>
#include<cstdlib>
#include<stack>
#include<queue>
#include<cmath>
#include<algorithm>
#include<functional>
#include<list>
#include<deque>
#include<bitset>
#include<set>
#include<map>
#include<unordered_map>
#include<cstring>
#include<sstream>
#include<complex>
#include<iomanip>
#include<numeric>
#define X first
#define Y second
#define pb push_back
#define rep(X,Y) for (int (X) = 0;(X) < (Y);++(X))
#define rrep(X,Y) for (int (X) = (Y-1);(X) >=0;--(X))
#define repe(X,Y) for ((X) = 0;(X) < (Y);++(X))
#define peat(X,Y) for (;(X) < (Y);++(X))
#define all(X) (X).begin(),(X).end()
#define rall(X) (X).rbegin(),(X).rend()

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
template<class T> using vv=vector<vector<T>>;
template<class T> ostream& operator<<(ostream &os, const vector<T> &t) {
os<<"{"; rep(i,t.size()) {os<<t[i]<<",";} os<<"}"<<endl; return os;}
template<class S, class T> ostream& operator<<(ostream &os, const pair<S,T> &t) { return os<<"("<<t.first<<","<<t.second<<")";}

int main(){
  ios_base::sync_with_stdio(false);
  cout<<fixed<<setprecision(0);
  int i,j,k;
  int h,w,f;
  cin>>h>>w;
  vector<string> s(h);
  rep(i,h)
    cin>>s[i];
  int n=0;
  rep(i,h)rep(j,w)n+=(s[i][j]=='#');
  rep(i,h)rep(j,w){
    vv<int> v(h,vector<int>(w));
    f=1;
    //cout<<pii(j,i);
    rep(y,h-i)if(f)rep(x,w-j){
	if((s[y][x]=='.') == (s[y+i][x+j]=='.')&&s[y][x]=='#'){
	  v[y][x]+=1; v[y+i][x+j]+=2;
	}
      }
    //cout<<f<<endl<<v;
    int a=0,b=0,c=0;
    rep(y,h)if(f)rep(x,w){
	if(v[y][x]==3)++c;
	if(v[y][x]==1)++a;
	if(v[y][x]==2)++b;
      }
    //cout<<a<<","<<b<<endl;
    if(f && abs(a-b)<=c && n==a+b+c){
      cout<<"YES"<<endl;
      return 0;
    }
  }
  cout<<"NO"<<endl;
  return 0;
}