Simple obfuscated

<?php
function
_O($__,$_O,$_0)
 { $__=1&&1!=0?' ':0;
$_o=$_O.$__.$_0; $_____
= $_o==$_O.$__.$_0?$_o.'!':
$_O; return $_____; } echo _O
('!!!!!!', 'hello', 'world'); ?>