#include <string>
#include <vector>
#include <algorithm>
#include <numeric>
#include <set>
#include <map>
#include <queue>
#include <iostream>
#include <sstream>
#include <cstdio>
#include <cmath>
#include <ctime>
#include <cstring>
#include <cctype>
#include <cassert>
#include <limits>
#include <functional>
#define rep(i,n) for(int (i)=0;(i)<(int)(n);++(i))
#define rer(i,l,u) for(int (i)=(int)(l);(i)<=(int)(u);++(i))
#define reu(i,l,u) for(int (i)=(int)(l);(i)<(int)(u);++(i))
#if defined(_MSC_VER) || __cplusplus > 199711L
#define aut(r,v) auto r = (v)
#else
#define aut(r,v) __typeof(v) r = (v)
#endif
#define each(it,o) for(aut(it, (o).begin()); it != (o).end(); ++ it)
#define all(o) (o).begin(), (o).end()
#define pb(x) push_back(x)
#define mp(x,y) make_pair((x),(y))
#define mset(m,v) memset(m,v,sizeof(m))
#define INF 0x3f3f3f3f
#define INFL 0x3f3f3f3f3f3f3f3fLL
using namespace std;
typedef vector<int> vi; typedef pair<int,int> pii; typedef vector<pair<int,int> > vpii; typedef long long ll;
template<typename T, typename U> inline void amin(T &x, U y) { if(y < x) x = y; }
template<typename T, typename U> inline void amax(T &x, U y) { if(x < y) x = y; }

template<typename T>
vector<pair<T,int> > runLength(const T a[], int n) {
	vector<pair<T,int> > r;
	if(n <= 0) return r;
	int cnt = 0;
	for(int i = 0; i <= n; i ++) {
		if(i == n || (i != 0 && a[i] != a[i-1])) {
			r.push_back(make_pair(a[i-1], cnt));
			cnt = 0;
		}
		cnt ++;
	}
	return r;
}

int main() {
	int H, W;
	scanf("%d%d", &H, &W);
	vector<char*> S(H);
	rep(i, H) S[i] = new char[W+1];
	rep(i, H) scanf("%s", S[i]);
	bool ans = false;
	rer(dy, 0, H-1) rer(dx, -W+1, W-1) if(dx > 0 || dy > 0) {
		bool ok = true;
		vector<vector<bool> > vis(H, vector<bool>(W, false));
		int cnt = 0;
		rep(i, H) rep(j, W) if(!vis[i][j]) {
			int len = 0;
			for(int yy = i, xx = j; yy < H && xx >= 0 && xx < W; yy += dy, xx += dx) {
				vis[yy][xx] = true;
				if(S[yy][xx] == '#') {
					++ len;
					++ cnt;
				}else {
					ok &= len % 2 == 0;
					len = 0;
				}
			}
			ok &= len % 2 == 0;
		}
		ok &= cnt > 0;
//		if(ok) cerr << dy << ", " << dx << endl;
		ans |= ok;
	}
	puts(ans ? "YES" : "NO");
	return 0;
}