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

#undef _P
#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(i,a,b) for (int i = (a); i < (b); i++)
#define RFOR(i,a,b) for (int i = (b)-1; i >= (a); i--)
#define REP(i,n) for (int i = 0; i < (n); i++)
#define RREP(i,n) for (int i = (n)-1; i >= 0; i--)
#define ALL(x) (x).begin(), (x).end()
#define ITR(x,c) for(__typeof(c.begin()) x=c.begin();x!=c.end();x++)
#define MP(x,y) make_pair((x), (y))
#define MIN(a,b) (a < b ? a : b)
#define MAX(a,b) (a > b ? a : b)
#define AMIN(a,b) if(b < a) (a) = (b)
#define AMAX(a,b) if(b > a) (a) = (b)
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
#define bitcount(b) __builtin_popcount(b)
#define GCD(a,b) (__gcd(a,b))
#define GCD3(a,b,c) (GCD(GCD(a,b), c))
#define LCM(a,b) (a/GCD(a,b)*b)
#define LCM3(a,b,c) LCM(LCM(a,b),c)
#define MOD 1000000007
typedef long long ll;
// -------------------------------------

int H, W;
string S[50];
bool m[50][50];

bool can(int dy, int dx) {
  ZERO(m);
  REP(y, H) {
    REP(x, W) {
      if (S[y][x] == '#') m[y][x] = true;
    }
  }

  REP(y, H) {
    REP(x, W) {
      if (m[y][x]) {
        if (y + dy >= H || x + dx >= W) return false;
        if (!m[y + dy][x + dx]) return false;
        m[y][x] = m[y + dy][x + dx] = false;
      }
    }
  }

  return true;
}

int main() {
  cin >> H >> W;
  REP(i, H) cin >> S[i];

  REP(dy, H) {
    REP(dx, W) {
      if (dy == 0 && dx == 0) continue;
      if (can(dy, dx)) {
        cout << "YES" << endl;
        return 0;
      }
    }
  }

  cout << "NO" << endl;

  return 0;
}