// takes S or L<S>
// doesn't reuse nodes so far
static Web webFromTriples2(O... l) {
  Web web = simpleWeb();
  for (int i = 0; i < l(l); i += 3) {
    WebNode a = web.newNode(), b = web.newNode();
    web_addLabels(a, get(l, i));
    web_addLabels(b, get(l, i+2));
    web_addLabels(web_getRelation(a, b), get(l, i+1));
  }
  ret web;
}