#include <iostream>
#include <algorithm>
using namespace std;

class range {private: struct I{int x;int operator*(){return x;}bool operator!=(I& lhs){return x<lhs.x;}void operator++(){++x;}};I i,n;
public:range(int n):i({0}),n({n}){}range(int i,int n):i({i}),n({n}){}I& begin(){return i;}I& end(){return n;}};

int h, w;

void nya(vector<string> &kort, int dr, int dc) {
  for(int r : range(h)) {
    for(int c : range(w)) {
      if(kort[r][c] != '#') { continue; }
      int nr = r + dr,
          nc = c + dc;
      if(nr < 0 || h <= nr || nc < 0 || w <= nc) { continue; }
      if(r == nr && c == nc) { continue; }
      if(kort[nr][nc] != '#') { continue; }
      kort[r][c] = 'R';
      kort[nr][nc] = 'B';
    }
  }
}

bool check(vector<string> kort) {
  int red = 0, blue = 0;
  for(int r : range(h)) {
    for(int c : range(w)) {
      if(kort[r][c] == '#') { return false; }
      if(kort[r][c] == 'R') { red++; }
      if(kort[r][c] == 'B') { blue++; }
    }
  }
  return red == blue && red > 0;
}

int main(void) {
  scanf("%d%d", &h, &w);
  vector<string> kort(h);
  for(int i : range(h)) { cin >> kort[i]; }
  for(int dr : range(-h, h)) {
    for(int dc : range(-w, w)) {
      vector<string> copy = kort;
      nya(copy, dr, dc);
      if(check(copy)) {
        puts("YES");
        return 0;
      }
    }
  }
  puts("NO");
  return 0;
}