# -*- coding: utf-8 -*-
from copy import deepcopy

h,w = map(int, input().split())
s = [list(input()) for _ in range(h)]

def check(dh,dw):
    s2 = deepcopy(s)
    for hi in range(h):
        for wi in range(w):
            if h>hi+dh>=0 and w>wi+dw>=0:
                if s2[hi][wi]=="#" and s2[hi+dh][wi+dw]=="#":
                    s2[hi][wi] = "r"
                    s2[hi+dh][wi+dw] = "b"
                elif s2[hi][wi]=="#":
                    return False
            elif s2[hi][wi]=="#":
                return False
    for hi in range(h):
        for wi in range(w):
            if s2[hi][wi]=="#":
                return False
    return True

for dh in range(h):
    for dw in range(w):
        if dh==0 and dw==0:
            continue
        if check(dh,dw):
            print("YES")
            exit()
print("NO")