Event.observe(window, "load", handle_searchoptions, false);
function handle_searchoptions() {
    $$(".so").each( function(element) {
       Event.observe(element, 'click', function() { $('alles').checked = false; });
    });
    Event.observe($('alles'), 'click', function() {
        $$(".so").each( function(element) { $(element.id).checked = false; });
    });
}