assertThat(copy.inverse().get(1)).isEqualTo("one");
    assertThat(copy.inverse().inverse()).isSameInstanceAs(copy);
  }

  @J2ktIncompatible
  @GwtIncompatible // SerializableTester
  public void testInverseSerialization() {
    ImmutableBiMap<String, Integer> bimap =
        ImmutableBiMap.copyOf(ImmutableMap.of(1, "one", 2, "two")).inverse();

        .inOrder();
    // backward map ordered by country
    assertThat(bimap.inverse().keySet())
        .containsExactly(Country.CANADA, Country.CHILE, Country.SWITZERLAND)
        .inOrder();
    // backward map ordered by country (even for currency values)
    assertThat(bimap.inverse().values())
        .containsExactly(Currency.DOLLAR, Currency.PESO, Currency.FRANC)
        .inOrder();
  }

        ImmutableListMultimap.<String, Integer>of().inverse());
    assertEquals(ImmutableListMultimap.of(1, "one"), ImmutableListMultimap.of("one", 1).inverse());
    assertEquals(
        ImmutableListMultimap.of(1, "one", 2, "two"),
        ImmutableListMultimap.of("one", 1, "two", 2).inverse());
    assertEquals(
        ImmutableListMultimap.of("of", 'o', "of", 'f', "to", 't', "to", 'o').inverse(),

      return oldValue;
    }
  }

  @LazyInit @RetainedWith private transient @Nullable BiMap<V, K> inverse;

  @Override
  public BiMap<V, K> inverse() {
    BiMap<V, K> result = inverse;
    return (result == null) ? inverse = new Inverse<>(this) : result;
  }

  private static final class Inverse<K extends @Nullable Object, V extends @Nullable Object>

        .isWithin(ALLOWED_ERROR)
        .of(x1 + xDelta);
    assertThat(transformation.slope()).isWithin(ALLOWED_ERROR).of(yDelta / xDelta);
    assertThat(transformation.inverse().slope()).isWithin(ALLOWED_ERROR).of(xDelta / yDelta);
    assertThat(transformation.inverse()).isSameInstanceAs(transformation.inverse());
    assertThat(transformation.inverse().inverse()).isSameInstanceAs(transformation);
  }

  /**

        ImmutableListMultimap.<String, Integer>of().inverse());
    assertEquals(ImmutableListMultimap.of(1, "one"), ImmutableListMultimap.of("one", 1).inverse());
    assertEquals(
        ImmutableListMultimap.of(1, "one", 2, "two"),
        ImmutableListMultimap.of("one", 1, "two", 2).inverse());
    assertEquals(
        ImmutableListMultimap.of("of", 'o', "of", 'f', "to", 't', "to", 'o').inverse(),

        ImmutableSetMultimap.<Integer, String>of(),
        ImmutableSetMultimap.<String, Integer>of().inverse());
    assertEquals(ImmutableSetMultimap.of(1, "one"), ImmutableSetMultimap.of("one", 1).inverse());
    assertEquals(
        ImmutableSetMultimap.of(1, "one", 2, "two"),
        ImmutableSetMultimap.of("one", 1, "two", 2).inverse());
    assertEquals(
        ImmutableSetMultimap.of('o', "of", 'f', "of", 't', "to", 'o', "to"),

        .isWithin(ALLOWED_ERROR)
        .of(x1 + xDelta);
    assertThat(transformation.slope()).isWithin(ALLOWED_ERROR).of(yDelta / xDelta);
    assertThat(transformation.inverse().slope()).isWithin(ALLOWED_ERROR).of(xDelta / yDelta);
    assertThat(transformation.inverse()).isSameInstanceAs(transformation.inverse());
    assertThat(transformation.inverse().inverse()).isSameInstanceAs(transformation);
  }

  /**

    assertEquals(HashBiMap.create(), bimap);
    bimap.put(Currency.DOLLAR, "dollar");
    assertThat(bimap.get(Currency.DOLLAR)).isEqualTo("dollar");
    assertEquals(Currency.DOLLAR, bimap.inverse().get("dollar"));
  }

  public void testCreateFromMap() {
    /* Test with non-empty Map. */
    Map<Currency, String> map =
        ImmutableMap.of(
            Currency.DOLLAR, "dollar",

    assertEquals(HashBiMap.create(), bimap);
    bimap.put(Currency.DOLLAR, "dollar");
    assertThat(bimap.get(Currency.DOLLAR)).isEqualTo("dollar");
    assertEquals(Currency.DOLLAR, bimap.inverse().get("dollar"));
  }

  public void testCreateFromMap() {
    /* Test with non-empty Map. */
    Map<Currency, String> map =
        ImmutableMap.of(
            Currency.DOLLAR, "dollar",