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

typedef long long ll;
typedef unsigned long long ull;
typedef vector<int> veci;
typedef vector<string> vecs;
template<class T,class U> using Hash=unordered_map<T,U>;

#define REP(i, a, n) for(ll i = a; i < n; i++)
#define RREP(i, a, n) for(ll i = n-1; i >= 0; i--)
#define rep(i, n) REP(i, 0, n)
#define rrep(i, n) RREP(i, 0, n)
#define MD 1000000007

template<class T> T read(){T a;cin >> a;return a;}
template<class T> T read(T& a){cin >> a;}
template<class T> void rarr(T a, int n){for(int i = 0; i < n; i++) {cin >> a[i];}}
template<class T> void write(T a){cout << a << endl;}
template<class T> void writes(vector<T> a, char* c = " "){cout << a[0];for(int i = 1; i < a.size(); i++)cout << c << a[i];cout << endl;;}
void write(double a){cout << fixed << setprecision(12) << a << endl;}
template<class T> void warr(T a, int n, char* c = " "){cout << a[0];for(int i = 1; i < n; i++)cout << c << a[i];cout << endl;}
void split(string s, string delim, veci& result){result.clear();string::size_type pos = 0;while(pos != string::npos){string::size_type p = s.find(delim, pos);if(p == string::npos){result.push_back(atoi(s.substr(pos).data()));break;}else {result.push_back(atoi(s.substr(pos, p - pos).data()));}pos = p + delim.size();}}
void split(string s, string delim, vecs& result){result.clear();string::size_type pos = 0;while(pos != string::npos){string::size_type p = s.find(delim, pos);if(p == string::npos){result.push_back(s.substr(pos));break;}else {result.push_back(s.substr(pos, p - pos));}pos = p + delim.size();}}
ll gcd(ll a, ll b){while(true){ll k = a % b;if(k == 0)return b;a = b;b = k;}}
ll comb(ll n, ll m){ll p=1;m=min(m,n-m);for(ll i=1;i<=m;i++){p*=n-i+1;p/=i;}return p;}

int main(void)
{
    int h,w;
    bool a[50][50]={0};
    int p=0;
    cin>>h>>w;
    rep(i,h){
        string s=read<string>();
        rep(j,w)
            if(s[j]=='#'){
                a[i][j]=true;
                p++;
            }
    }
    if(p==0||p%2==1){
        write("NO");
        exit(0);
    }
    p/=2;
    string res="NO";
    REP(y,0,h+1){
        REP(x,-w,w+1){
            if(y==0&&x==0)continue;
            int b[50][50]={0};
            int t=0;
            rep(i,h){
                if(i+y<0||i+y>=h)continue;
                rep(j,w){
                    if(j+x<0||j+x>=w)continue;
                    if(a[i][j]&&a[i+y][j+x]&&!b[i][j]){
                        b[i][j]=b[i+y][j+x]=true;
                        t++;
                    }
                }
            }
            //cout<<x<<" "<<y<<" "<< t<<endl;
            if(t==p)res="YES";
        }
    }
    write(res);
	return 0;
}