#include "bits/stdc++.h"
#define REP(i,n,N) for(int i=(n); i<(N); i++)
#define RREP(i,n,N) for(int i=(N-1); i>=n; i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define ALL(v) (v).begin(),(v).end()
#define p(s) cout<<(s)<<endl
#define p2(a,b) cout<<(a)<<" "<<(b)<<endl
typedef long long ll;
using namespace std;
const int inf=1e9;

int H,W;
vector<string> s;
int main(void) {
    cin >> H >> W;
    bool ok=false;
    REP(i, 0, H){
        string a;
        cin >> a;
        s.push_back(a);
        if(s[i].find("#")!=string::npos){
            ok=true;
        }
    }
    if(!ok) {
        p("NO");
        return 0;
    }
    REP(dy, -H, H){
        REP(dx, -W, W) {
            if (dx == 0 && dy == 0) continue;
            auto ss = s;
            bool ng = false;
            REP(i,0,H){
                REP(j,0,W){
                    if(ss[i][j]!='#') continue;
                    int ny = i + dy;
                    int nx = j + dx;
                    if(!CK(ny,0,H)||!CK(nx,0,W)) {
                        ng=true;
                        break;
                    }
                    if(ss[ny][nx]=='#'){
                        ss[ny][nx]='.';
                    }else{
                        ng=true;
                        break;
                    }
                }
                if(ng) break;
            }
            if(!ng){
                p("YES");
                return 0;
            }
        }
    }
    p("NO");
    return 0;
}