@GwtCompatible
@NullMarked
class LegacyComparable implements Comparable, Serializable {
  static final LegacyComparable X = new LegacyComparable("x");
  static final LegacyComparable Y = new LegacyComparable("y");
  static final LegacyComparable Z = new LegacyComparable("z");

  static final Iterable<LegacyComparable> VALUES_FORWARD = asList(X, Y, Z);
  static final Iterable<LegacyComparable> VALUES_BACKWARD = asList(Z, Y, X);