import strutils, sequtils, algorithm, math

proc solve(): string =
  var
    hw = readLine(stdin).split(' ').map(parseInt)
    board = newSeq[string](hw[0])
    tBoard = newSeq[string](hw[0])
    count = 0
    tmpCount: int
    flag = false

  for i in countup(0, hw[0] - 1):
    board[i] = readLine(stdin)
    count += board[i].count('#')

  if count mod 2 == 1:
    return "NO"

  for hMove in countup(0, hw[0] - 1):
    for wMove in countup(-hw[1] + 1, hw[1] - 1):
      tmpCount = 0
      flag = false
      for h in countup(0, hw[0] - 1):
        tBoard[h] = board[h]
      for h in countup(0, hw[0] - 1):
        if hMove + h >= hw[0]:
          break
        for w in countup(0, hw[1] - 1):
          if wMove + w >= hw[1] or wMove + w < 0:
            break
          if tBoard[h][w] == '#':
            if tBoard[hMove + h][wMove + w] == '#':
              tmpCount += 1
              tBoard[h][w] = 'R'
              tBoard[hMove + h][wMove + w] = 'B'
            else:
              flag = true
              break
          # else:
          #   flag = true
          #   break
        if flag:
          break
      if tmpCount == count div 2 and not flag:
        return "YES"
  return "NO"

echo(solve())