static Set<S> nlLogic_allLHSEvalFragments(L<IfThen> rules) {
  final new TreeSet<S> set;
  nlLogic_visit(collect(rules, 'in), voidfunc(O o) {
    if (o cast Func) if (eq(o.name, 'eval)) set.add(o.arg.text());
  });
  ret set;
}