import sequtils,strutils,algorithm,math,sugar,macros,strformat

proc getchar_unlocked():char {. importc:"getchar_unlocked",header: "<stdio.h>" .}
proc scan(): int =
  while true:
    var k = getchar_unlocked()
    if k < '0' or k > '9': break
    else: result = 10 * result + k.ord - '0'.ord

let h = scan()
let w = scan()
var S = newSeqWith(w,newSeqWith(h,false))
var blockSum = 0
for y in 0..<h:
  for x in 0..<w:
    let s = getchar_unlocked() == '#'
    S[x][y] = s
    if s : blockSum += 1
  discard getchar_unlocked()

if blockSum <= 1: quit "NO",0
proc check(sx,sy:int) =
  var already = newSeqWith(w,newSeqWith(h,false))
  for x in 0..<w:
    for y in 0..<h:
      if not S[x][y] : continue
      if already[x][y]:continue
      if x + sx >= w or y + sy >= h : return
      if not S[x+sx][y+sy]: return
      already[x+sx][y+sy] = true
  quit "YES",0

for x in 0..<w:
  for y in 0..<h:
    if x == 0 and y == 0 : continue
    check(x,y)
echo "NO"