void main() {
    Set<String> vowels = Set.of("a", "e", "i", "o", "u");

    IO.println(vowels.contains("e"));
    IO.println(vowels.size());

    Set<String> guests = new HashSet<>();
    guests.add("Ada");
    guests.add("Grace");
    guests.add("Ada");
    IO.println(guests.size());

    ArrayList<Integer> numbers = new ArrayList<>(List.of(1, 2, 2, 3, 3, 3, 4));
    Set<Integer> unique = new TreeSet<>(numbers);
    IO.println(unique);
    IO.println(unique.size());
}

// From Groundwork, chapter 9 (ch09-maps-and-sets), box 13.
// This example is from Groundwork, licensed CC BY-NC-SA 4.0.
// Run with: java ch09_13.java