import sys
import copy

input = sys.stdin.readline

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

for dy in range(h):
 for dx in range(w):
  if dy == 0 and dx == 0:
   continue
  sc = copy.deepcopy(s)
  flag = True
  for i in range(h):
   for j in range(w):
    if sc[i][j] == '#':
     if i + dy >= h or j + dx >= w or sc[i+dy][j+dx] == '.':
      flag = False
      break
     else:
      sc[i+dy][j+dx] = '.'
   if not flag:
    break
  if flag:
   print('YES', end='')
   exit()
print('NO', end='')