import Data.Char
import Data.Bool
import Data.List
import Control.Monad

main = do
 [h,w] <- map read . words <$> getLine
 is <- map (\i -> i + (div i w * w)) . findIndices (=='#') . filter isPrint <$> getContents
 putStrLn $ bool "NO" "YES" (dpaint h w is)

dpaint h w is
 | odd (length is) = False
 | otherwise = or $ do
  d <- [1 .. (h*w-1)]
  let is' = map (+d) is
  let inter = intersect is is'
  let inter' = map (subtract d) inter
  return (sort (inter++inter') == is)