const Link *List::tail() const { Link *l = _tail; while ( l && !l->active() ) l = l->prev(); return l; }
const Link *List::head() const { Link *l = _head; while ( l && !l->active() ) l = l->next(); return l; }
const Link *List::tail() const { Link *l = _tail; while ( l && !l->active() ) l = l->prev(); return l; }
const Link *List::head() const { Link *l = _head; while ( l && !l->active() ) l = l->next(); return l; }