import Control.Applicative ((<$>))
import Control.Monad (replicateM, guard)
import Data.List (delete)

main :: IO ()
main = do
  [h, w] <- map read <$> words <$> getLine
  solve h w <$> replicateM h getLine >>= putStrLn

solve :: Int -> Int -> [String] -> String
solve h w xs | null ls = "NO"
             | any (f ls) [(di,dj)| dj <- [0..h-1], di <- [1-w..w-1]] = "YES"
             | otherwise = "NO"
  where ls = do
          j <- [0..h-1]
          i <- [0..w-1]
          guard $ xs !! j !! i == '#'
          return (i, j)
        f [] (di, dj) = True
        f ((i, j):rs) (di, dj) | (i+di, j+dj) `elem` rs = f (delete (i+di, j+dj) rs) (di, dj)
                               | otherwise = False