#include <iostream>
#include <algorithm>
#include <functional>
#include <string>
#include <limits.h>
#include <vector>
#include <numeric>
using namespace std;

int main(){
	int h,w;
	string in;
	int data[50][50];
	int data2[50][50];
	int lowy = 999;
	int lowx = 999;
	int highy = -1;
	int highx = -1;
	int ysize,xsize;
	bool check;
	
	cin >> h >> w;
	for(int iy=0; iy<h; iy++){
		cin >> in;
		for(int ix=0; ix<w; ix++){
			if(in[ix] == '#'){
				data[iy][ix] = 1;
				if(iy < lowy){
					lowy = iy;
				}
				if(ix < lowx){
					lowx = ix;
				}
				if(iy > highy){
					highy = iy;
				}
				if(ix > highx){
					highx = ix;
				}
			}else{
				data[iy][ix] = 0;
			}
		}
	}
	
	ysize = (highy - lowy) / 2;
	xsize = (highx - lowx) / 2;
	
	for(int ysizei=0; ysizei<=ysize; ysizei++){
		for(int xsizei=0; xsizei<=xsize; xsizei++){
			//初期化
			for(int iy=0; iy<h; iy++){
				for(int ix=0; ix<w; ix++){
					data2[iy][ix] = data[iy][ix];
				}
			}
			check = true;
			
			if(ysizei != 0 || xsizei != 0){
				for(int iy=0; iy<h; iy++){
					for(int ix=0; ix<w; ix++){
						if(data2[iy][ix] == 1){
							data2[iy][ix] = 0;
							if(data2[iy+ysizei][ix+xsizei] == 0){
								check = false;
								iy = h;
								break;
							}else{
								data2[iy+ysizei][ix+xsizei] = 0;
							}
						}
					}
				}
				
				if(check){
					ysizei = ysize;
					break;
				}
			}
		}
	}
	
	if(check){
		cout << "YES" << endl;
	}else{
		cout << "NO" << endl;
	}
	
	return 0;
}