docs: public static <K1, K2, V1 extends K2, V2> ImmutableSetMultimap<K1, V2> composeToSetMultimapStrictly(
        final Multimap<K1, V1> first, final Multimap<K2, V2> second) {
      checkArgument(second.keySet().containsAll(first.values()));
      return composeToSetMultimap(first, second);
    }