function Buttonleiste()
{
  if(screen.height <= 600)
    var bsl = window.open("button/button_l.htm","button_l",",");
  else
    var bbl = window.open("button/buttonb_l.htm","button_l",",");
  if(screen.height <= 600)
    var bsr = window.open("button/button_r.htm","button_r",",");
  else
    var bbr = window.open("button/buttonb_r.htm","button_r",",");
}