h, w = gets.not_nil!.split(" ").map{|x| x.to_i}
rect = [] of Array(String)
1.upto(h) do |i|
  rect << gets.not_nil!.split("")
end

def ok?(rect, h, w)
  0.upto(h-1) do |dy|
    0.upto(w-1) do |dx|
      if dx == 0 && dy == 0
        next
      end

      _rect = rect.clone
      ok = true

      0.upto(h-1) do |y|
        0.upto(w-1) do |x|
          if _rect[y][x] == "."
            next
          end

          ny = y + dy
          nx = x + dx

          if nx >= w || ny >= h
            next
          end

          if _rect[y][x] == _rect[ny][nx]
            _rect[y][x] = "."
            _rect[ny][nx] = "."
          else
            ok = false
            break
          end

        end
      end

      0.upto(h-1) do |y|
        0.upto(w-1) do |x|
          if _rect[y][x] == "#"
            ok = false
          end
        end
      end

      if ok
        return true
      end
    end
  end
  return false
end

puts ok?(rect, h, w) ? "YES" : "NO"