from collections import *
from itertools import *
from functools import *
from heapq import *
import sys,math
input = sys.stdin.readline

H,W = map(int,input().split())
S = [list(input())[:-1] for _ in range(H)]

for i in range(H):
    for j in range(W):
        S[i][j]=int(S[i][j]=='#')
        
        

def check(x,y):
    
    T = [[0]*(2*W) for _ in range(2*H)]
    for i in range(H):
        for j in range(W):
            T[i][j] += S[i][j]
            T[i+x][j+y] += S[i][j]
            
            
    flg = True
    a = 0
    b = 0
    for i in range(H):
        for j in range(W):
            if (S[i][j]==1):
                if T[i][j]==1:
                    a += 1
                    if T[i+x][j+y]!=2:
                        flg = False
                if (T[i][j]==2):
                    b += 1
            elif T[i][j]!=0:
                flg = False
    return flg&(a==b)
    
for x in range(H):
    for y in range(W):
        if x+y==0:
            continue
        if check(x,y):
            print('YES')
            exit()
print('NO')