deselezionare i radio button

[br1]

<SCRIPT LANGUAGE="JavaScript">
<!--
var ls;
function sw(chi){
	if(chi==ls) {
		ls = null;
		chi.checked = false;
		return false;
	}
	ls = chi;	 
}
//-->
</SCRIPT>
...
<form>
<input type=radio name=pippo onclick="sw(this)">
<input type=radio name=pippo onclick="sw(this)">
</form>