#include <bits/stdc++.h>
using namespace std;
int main() {
  int H, W;
  cin >> H >> W;
  char tmp;
  int S[H][W];
  for (int i = 0; i < H; i++) {
    for (int j = 0; j < W; j++) {
      cin >> tmp;
      if (tmp == '#')
        S[i][j] = 1;
      else
        S[i][j] = 0;
    }
  }
  int NG = 0;
  for (int i = 0; i < H; i++) {
    for (int j = 0; j < W; j++) {
      if (S[i][j] == 1) {
        if ((j + 1) < W) {
          S[i][j] += S[i][j + 1];
        }
        if ((i + 1) < H) {
          S[i][j] += S[i + 1][j];
        }
        if ((j - 1) >= 0) {
          S[i][j] += S[i][j - 1];
        }
        if ((i - 1) >= 0) {
          S[i][j] += S[i - 1][j];
        }
      }
    }
  }
  for (int i = 0; i < H; i++) {
    for (int j = 0; j < W; j++) {
      if (S[i][j] == 1) {
        NG = 1;
        break;
      }
    }
  }
  if (NG == 0)
    cout << "yes" << endl;
  else
    cout << "no" << endl;
  return 0;
}
