import java.util.Scanner;


public class Main_yukicoder179 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int h = sc.nextInt();
        int w = sc.nextInt();

        char[][] s = new char[h][];
        int black = 0;
        for (int i = 0; i < h; i++) {
        	s[i] = sc.next().toCharArray();
        	for (int j = 0; j < s[i].length; j++) {
        		if (s[i][j] == '#') {
        			black++;
        		}
        	}
        }

        boolean flag = false;
        if (black != 0 && black % 2 == 0) {
        	fin:
        	for (int dx = - w + 1; dx <= w - 1; dx++) {
            	for (int dy = - h + 1; dy <= h - 1; dy++) {
            		int same = 0;
//            		next:
            		for (int i = 0; i < h; i++) {
            			for (int j = 0; j < w; j++) {
            				if (i + dy >= 0 && i + dy < h && j + dx >= 0 && j + dx < w) {
//            					if (s[i][j] != s[i + dy][j + dx]) {
//            						break next;
//            					}
            					if (s[i][j] == '#' && s[i + dy][j + dx] == '#') {
            						same++;
            					}
            				}
            			}
            		}
            		
            		if (same == (black / 2)) {
            			boolean[][] used = new boolean[h][w];
                		flag = true;
                		for (int i = 0; i < h; i++) {
                			for (int j = 0; j < w; j++) {
                				if (i + dy >= 0 && i + dy < h && j + dx >= 0 && j + dx < w) {
                					if (s[i][j] == '#' && !used[i][j]) {
                						if (s[i + dy][j + dx] == '#' && !used[i + dy][j + dx]) {
                							used[i][j] = true;
                							used[i + dy][j + dx] = true;
                						} else {
                							flag = false;
                						}
                					}
                				}
                			}
                		}

                		if (flag) {
//                			System.out.println(dx + " " + dy);
                			break fin;
                		}
            		}
            	}
        	}
        }

        if (flag) {
        	System.out.println("YES");
        } else {
        	System.out.println("NO");
        }

        sc.close();
    }
}