function header(){

  var d = new Date();
  var h = d.getHours(); 

  if (h >= 7 && h < 13)       { m = "desayuno"; } 
  else if (h >= 13 && h < 20) { m = "comida"; }
  else                        { m = "cena"; }   
  
  return "/images/headers/"+m+"/3.gif";
}