Extreme minification of shortest possible PSR-0 compliant autoloader, 5 lines !

l.php

<?php
//set_include_path(get_include_path() . PATH_SEPARATOR . __DIR__); // optional
spl_autoload_register(function ($class) {
	$file = preg_replace('#\\\|_(?!.+\\\)#','/', $class) . '.php';
	if (stream_resolve_include_path($file))
		require $file;
});