// should be thread-safe by nature

// compare efficiently due to md5 caching

// tested with A = S

static class ImmL<A> extends AbstractList<A> {

  new L<A> l;

  int hash;

  S md5;

  *() {}

  *(L<A> _l) { l.addAll(_l); }

  // List methods

  public int size() {

    ret l.size();

  }

  public A get(int i) {

    ret l.get(i);

  }

  public synchronized int hashCode() {

    if (hash == 0)

      hash = l.hashCode();

    ret hash;

  }

  public bool equals(O o) {

    if (o instanceof ImmL

      && neq(md5(), ((ImmL) o).md5()))

      false;

    ret super.equals(o);

  }

  public synchronized S md5() {

    if (md5 == null)

      md5 = main.md5(structure(l));

    ret md5;

  }

}