static Elements filterOut(Collection<Element> elements, Collection<Element> outs) {
        Elements output = new Elements();
        for (Element el : elements) {
            boolean found = false;
            for (Element out : outs) {
                if (el.equals(out)) {
                    found = true;
                    break;
                }
            }
            if (!found)
                output.add(el);
        }
        return output;
    }