#!/usr/bin/env PyPy3

from collections import Counter, defaultdict, deque
import itertools
import re
import math
from functools import reduce
import operator
import bisect
from heapq import *
import functools

mod=10 ** 9 + 7

import sys
input = sys.stdin.readline

h,w=map(int,input().split())
s = [input().rstrip() for _ in range(h)]
li = []
for i in range(h):
    for j in range(w):
        if s[i][j] == '#':
            li.append((i,j))
if len(li) % 2:
    print('NO')
else:
    for i in range(1,len(li)):
        px = li[i][0] - li[0][0]
        py = li[i][1] - li[0][1]
        ns = [[0] * w for _ in range(h)]
        flg = 0
        for j in range(h):
            for k in range(w):
                if s[j][k] == '#':
                    if ns[j][k]:
                        continue
                    ns[j][k] = 1
                    if 0 <= j + px < h and 0 <= k + py < w:
                        if s[j + px][k + py] == '#' and ns[j + px][k + py] == 0:
                            ns[j + px][k + py] = 1
                        else:
                            flg = 1
                            break
                    else:
                        flg = 1
                        break
            if flg:
                break
        if not flg:
            print('YES')
            exit()
    print('NO')