def main():
    from math import sqrt,sin,cos,tan,ceil,radians,floor,gcd,exp,log,log10,log2,factorial,fsum
    from heapq import heapify, heappop, heappush
    from bisect import bisect_left, bisect_right
    from copy import deepcopy
    import copy
    import random
    from collections import deque,Counter,defaultdict
    from itertools import permutations,combinations
    from decimal import Decimal,ROUND_HALF_UP
    #tmp = Decimal(mid).quantize(Decimal('0'), rounding=ROUND_HALF_UP)
    from functools import lru_cache, reduce
    #@lru_cache(maxsize=None)
    from operator import add,sub,mul,xor,and_,or_,itemgetter
    INF = 10**18
    mod1 = 10**9+7
    mod2 = 998244353
    
    #DecimalならPython
    
    
    '''
    H,Wが小さい
    4重ループまでは回る
    最左上を赤で塗るとして、そこからどう平行移動するのかを全探索する
    
    '''
    
    H,W = map(int, input().split())
    S = [list(input()) for _ in range(H)]
    
    sy = -1
    sx = -1
    
    for i in range(H):
        for j in range(W):
            if S[i][j] == '#':
                sy = i
                sx = j
                break
    
    if sy == -1:
        print('NO')
        exit()
    
    for dy in range(H):
        for dx in range(W):
            
            if dy == dx == 0:
                continue
            
            T = deepcopy(S)
            f = True
            
            for i in range(H):
                for j in range(W):
                    if T[i][j] == '#':
                        if i+dy>=H or j+dx>=W:
                            f = False
                            break
                        
                        if T[i+dy][j+dx] == '#':
                            T[i][j] = '.'
                            T[i+dy][j+dx] = '.'
                        else:
                            f = False
                            break
                
                else:
                    continue
                break
            
            for i in range(H):
                for j in range(W):
                    if T[i][j] == '#':
                        f = False
                        break
                else:
                    continue
                break
            
            if f:
                print('YES')
                exit()
    
    print('NO')
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
if __name__ == '__main__':
    main()