h, w = [int(x) for x in input().split()]

tiles = []

for i in range(h):
  l = input()
  for j in range(w):
    if l[j] == "#":
      tiles.append((i, j))

vec = []

for i in range(h):
  for j in range(-1 * w + 1 ,w):
    vec.append((i, j))

del vec[vec.index((0, 0))]

tiles_num = len(tiles)
      
if tiles_num == 0:
  print("NO")
else:
  
  result = False
  
  for v in vec:
    ans = set()
    ans_num = 0
    
    for t in tiles:
      
      ot = (t[0] + v[0], t[1] + v[1])
      
      if t not in ans:
        if ot in tiles:
          if ot not in ans:
            ans.add(t)
            ans.add(ot)
            ans_num += 2
    
    if tiles_num == ans_num:

      result = True
      break
  
  if result:
    print("YES")
  else:
    print("NO")