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

int main()
{
    int H, W; cin>>H>>W;
    vector<string> S(H);

    int N=0;
    for(auto& e: S) {
        cin>>e;
        N+=count(begin(e), end(e), '#');
    }

#define REP(i, a, b) for(int i=a; i<b; ++i)
    
    REP(r, -H, H) REP(c, -W, W) if (c|r) {
        auto T=S;
        int red=0, blue=0;
        REP(i, 0, H) REP(j, 0, W) {
            if (!(T[i][j]=='#' && 0<=i+r && i+r<H && 0<=j+c && j+c<W)) continue;
            if (T[i][j]==T[i+r][j+c]) {
                T[i][j]=0;
                T[i+r][j+c]=1;
                ++red;
                ++blue;
            }
        }
        if (red==blue && N==red+blue)
            return !printf("YES\n");
    }
    puts("NO");
}