public boolean equals(@Nullable Object obj) {
      if (obj instanceof SameCharacterInstance) {
        SameCharacterInstance that = (SameCharacterInstance) obj;
        return i == that.i;
      }
      return false;
    }
  }

  static class SameBooleanInstance {
    private final Boolean i;

    public SameBooleanInstance(Boolean i) {
      this.i = checkNotNull(i);