static <A> L<A> syncTakeFirst(Cl<A> l, int n) {
  if (l == null) ret takeFirst(l, n);
  synchronized(collectionMutex(l)) {
    ret takeFirst(l, n);
  }
}

static <A> L<A> syncTakeFirst(int n, Cl<A> l) {
  ret syncTakeFirst(l, n);
}