Quick synthax question

Quick synthax question

I use this to fade things outside the category I select...
  1. jQuery(document).ready(function($){
  2.         $("#categories a").click(function() {
  3.             var cat = $(this).attr('class');
  4.             $("#wrapper div").fadeTo(50, 0.2);
  5.             $("#wrapper div").filter('.'+cat).fadeTo(50, 1);
  6.             return false;
  7.         });
  8.         $("#categories a.all").click(function() {
  9.             $("#grid-wrapper div").fadeTo(50, 1);
  10.         });
  11. });
But I would like to replace line 4 to fade only things that are not in the category. What synthax should I use ?

Many thanks for your time and help ;-)