from itertools import *
from bisect import *
# from math import *
from collections import *
from heapq import *
from random import *
from decimal import *
import numpy as np
import sys
import copy

sys.setrecursionlimit(10 ** 6)
int1 = lambda x: int(x) - 1
p2D = lambda x: print(*x, sep="\n")
def II(): return int(sys.stdin.readline())
def MI(): return map(int, sys.stdin.readline().split())
def MI1(): return map(int1, sys.stdin.readline().split())
def MF(): return map(float, sys.stdin.readline().split())
def LI(): return list(map(int, sys.stdin.readline().split()))
def LI1(): return list(map(int1, sys.stdin.readline().split()))
def LF(): return list(map(float, sys.stdin.readline().split()))
def LLI(rows_number): return [LI() for _ in range(rows_number)]
dij = [(1, 0), (0, 1), (-1, 0), (0, -1)]

def main():
    def check(di,dj):
        for i in range(h):
            for j in range(w):
                if t[i][j] and first[i][j]:
                    if not 0<=i+di<h:return False
                    if not 0<=j+dj<w:return False
                    if not t[i+di][j+dj]:return False
                    first[i+di][j+dj]=False
        return True

    h, w = MI()
    t = [[c == "#" for c in input()] for _ in range(h)]
    si,sj=-1,-1
    for i in range(h):
        for j in range(w):
            if t[i][j]:
                if si==-1:
                    si,sj=i,j
                else:
                    first=[[True]*w for _ in range(h)]
                    if check(i-si,j-sj):
                        print("YES")
                        exit()
    print("NO")
main()