static <A> Cl<HasIndex> indicesOf_collectionOfHasIndex(L<A> l, A a) {
  if (l == null) null;
  
  ifclass IContentsIndexedList2
  if (l cast IContentsIndexedList2)
    ret l.indicesOf_treeSetOfHasIndex(a);
  endif
  
  new L<HasIndex> x;
  int n = l(l);
  for (int i = 0; i < n; i++)
    if (eq(l.get(i), a))
      x.add(HasIndex(i));
  ret x;
}