if(document.images) {
    bon = new Image
    bou = new Image
    bon.src = '_images/menu_on.gif'
    bou.src = '_images/menu_off.gif'
  } 
else {
    bon = ""
    bou = ""
    document.a = ""
    document.b = ""
    document.c = ""
    document.d = ""
    document.e = ""
    document.f = ""
    document.g = ""
    document.k = ""

    document.wstecz = ""
    document.top = ""

    document.t = ""
    document.u = ""
    document.w = ""
    document.x = ""
    document.y = ""
    document.z = ""
  }