function switch_to_main() {
  notmain = document.getElementById("notmainthreads");
  main    = document.getElementById("mainthreads");
  notmain.style.display = "none";
  main.style.display    = "block";
  fadeIn('category_main', '#ffffff');
}

function switch_to_notmain() {
  notmain = document.getElementById("notmainthreads");
  main    = document.getElementById("mainthreads");
  notmain.style.display = "block";
  main.style.display    = "none";
  fadeIn('category_notmain','#ffffff');
}