"""

https://yukicoder.me/problems/no/179

ずらし方全探索

"""

import sys

def check(dx,dy):
    
    for i in range(H):
        for j in range(W):

            if S[i][j] == ".":
                continue

            cnt = 0

            if 0 <= i+dx < H and 0 <= j+dy < W and S[i+dx][j+dy] == "#":
                cnt += 1
            if 0 <= i-dx < H and 0 <= j-dy < W and S[i-dx][j-dy] == "#":
                cnt += 1

            if cnt != 1:
                return False

    return True
            

H,W = map(int,input().split())

S = [ input() for i in range(H) ]

for dx in range(51):

    for dy in range(-50,51):

        if check(dx,dy):
            print ("YES")
            sys.exit()

print ("NO")