Bug in Tutorial

In the "Getting Started with jQuery" tutorial, I downloaded the jQuery
Starterkit.
Within that StarterKit was a custom.js file containing the following:
jQuery(document).ready(function() {
// do something here
});
Firebug reported an error: jQuery unknown. As I just finished the
"How It Works" tutorial, I knew that custom.js should be:
$(document).ready(function() {
// do something here
});