#include <assert.h>
#include <ctype.h>
#include <float.h>
#include <limits.h>
#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>

#include <algorithm>
#include <bitset>
#include <complex>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <vector>
using namespace std;

#define SZ(a) (int)(a).size()
#define FOR(i,a,b) for (int i=(a); i<=(b); ++i)
#define REP(i,n) for (int i=0; i<(n); ++i)
#define ALL(c) c.begin(), c.end()
#define CLR(c,n) memset(c, n, sizeof(c))
#define MCPY(d, s) memcpy(d, s, sizeof(d))
#define TR(it, c) for (auto it = c.begin();it != c.end(); ++it)
#define CONTAIN(it, c) (c.find(it) != c.end())
typedef vector<int> VI;
typedef pair<int, int> PII;
template <class T> void checkmin(T &a, T b) { if (b<a) a=b; }
template <class T> void checkmax(T &a, T b) { if (b>a) a=b; }
typedef long long LL;
const int INF=0x3F3F3F3F;

PII x[2500];
int n;
#define X first
#define Y second
PII operator+(PII p, PII q) { return PII(p.X+q.X, p.Y+q.Y); }
PII operator-(PII p, PII q) { return PII(p.X-q.X, p.Y-q.Y); }

struct PIIHash {
  size_t operator()(PII p) const {
    return hash<int>()(p.X)^hash<int>()(p.Y);
  }
};
bool check(PII diff) {
  unordered_set<PII, PIIHash> s(x, x+n);
  while (!s.empty()) {
    PII b=*s.begin();
    int cnt = 0;
    for (PII p = b; CONTAIN(p, s); p = p + diff) {
      s.erase(p);
      ++cnt;
    }
    for (PII p = b - diff; CONTAIN(p, s); p = p - diff) {
      s.erase(p);
      ++cnt;
    }
    if (cnt % 2 == 1) return false;
  }
  return true;
}

bool go() {
  if (n % 2 == 1) return false;
  for (int i = 1; i < n; ++i) {
    if (check(x[i]-x[0])) return true;
  }
  return false;
}
int main(int argc, char *argv[]) {
  int w, h;
  char s[64];
  while (scanf("%d%d", &h, &w) == 2) {
    n = 0;
    REP(i, h) {
      scanf("%s", s);
      REP(j, w) if (s[j] == '#') x[n++] = PII(i, j);
    }
    printf("%s\n", go() ? "YES" : "NO");
  }
}