require 'set'

H, W = gets.split.map(&:to_i)

class << MAP = Array.new(H) { gets.strip }
  def ok?(dx, dy)
    d = dy * W + dx
    bs = blacks - blacks.map {|i| i + d }
    bs.size == blacks.size / 2 && bs.all? {|i| flat[i + d] == 35 }
  end

  def solve
    ax, ay, bx, by = aabb
    (1..bx - ax).each do |dx|
      (1..by - ay).each do |dy|
        return :YES if ok?(dx, dy)
      end
    end
    :NO
  end

  def flat
    @flat ||= map(&:bytes).flatten
  end

  def blacks
    @blacks ||= Set.new(flat.each_with_index.map {|cell, i| i if cell == 35 }.compact)
  end

  def aabb
    ax = ay = bx = by = nil
    blacks.each do |i|
      y, x = i.divmod(W)
      ax = x if !ax || ax > x
      ay = y if !ay || ay > y
      bx = x if !bx || bx < x
      by = y if !by || by < y
    end
    return ax, ay, bx, by
  end
end

puts MAP.solve