static <A, B> L<A> topTenKeysByValue(Map<A, B> map) {
  ret topTenKeysByValue(10, map);
}

static <A, B> L<A> topTenKeysByValue(int n, Map<A, B> map) {
  ret takeFirst_cloneIfDifferent(n, keysSortedByValueDesc(map));
}