* first permutation will be in ascending order, and the last will be in descending order.
   *
   * <p>Elements that compare equal are considered equal and no new permutations are created by
   * swapping them.
   *
   * <p>An empty iterable has only one permutation, which is an empty list.
   *
   * @param elements the original iterable whose elements have to be permuted.

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableBiMap} whose keys
   * and values are the result of applying the provided mapping functions to the input elements.
   * Entries appear in the result {@code ImmutableBiMap} in encounter order.
   *
   * <p>If the mapped keys or values contain duplicates (according to {@link

    tentativeArgs.set(i, alternateArg);
    return createInstance(factory, tentativeArgs).hashCode()
        == createInstance(factory, args).hashCode();
  }

  // distinctValues is a type-safe class-values mapping, but we don't have a type-safe data
  // structure to hold the mappings.
  @SuppressWarnings({"unchecked", "rawtypes"})
  private FreshValueGenerator newFreshValueGenerator() {
    FreshValueGenerator generator =

          // Four byte characters
          FOUR_BYTE_ROUNDTRIPPABLE_CHARACTERS;

  /** Tests that round tripping of all two byte permutations work. */
  @GwtIncompatible // java.nio.charset.Charset
  public void testIsWellFormed_1Byte() {
    testBytes(1, EXPECTED_ONE_BYTE_ROUNDTRIPPABLE_COUNT);
  }

  /** Tests that round tripping of all two byte permutations work. */
  @GwtIncompatible // java.nio.charset.Charset

   */

  /**
   * Creates an {@code ArrayTable} with the mappings in the provided table.
   *
   * <p>If {@code table} includes a mapping with row key {@code r} and a separate mapping with
   * column key {@code c}, the returned table contains a mapping with row key {@code r} and column
   * key {@code c}. If that row key / column key pair in not in {@code table}, the pair maps to
   * {@code null} in the generated table.

   * close or flush the reader.
   *
   * <p>This is identical to {@link #copy(Readable, Appendable)} but optimized for these specific
   * types. CharBuffer has poor performance when being written into or read out of so round tripping
   * all the bytes through the buffer takes a long time. With these specialized types we can just
   * use a char array.
   *
   * @param from the object to read from
   * @param to the object to write to

   *
   * <p>Files are mapped from offset 0 to its length.
   *
   * <p>This only works for files ≤ {@link Integer#MAX_VALUE} bytes.
   *
   * @param file the file to map
   * @param mode the mode to use when mapping {@code file}
   * @return a buffer reflecting {@code file}
   * @throws FileNotFoundException if the {@code file} does not exist
   * @throws IOException if an I/O error occurs
   * @see FileChannel#map(MapMode, long, long)

  /**
   * Returns a {@link Collector} that accumulates elements into an {@code ImmutableMap} whose keys
   * and values are the result of applying the provided mapping functions to the input elements.
   * Entries appear in the result {@code ImmutableMap} in encounter order.
   *
   * <p>If the mapped keys contain duplicates (according to {@link Object#equals(Object)}, an {@code

     * unmodifiable map with each of the entries. For example, {@code
     * Splitter.on(';').trimResults().withKeyValueSeparator("=>").split("a=>b ; c=>b")} will return
     * a mapping from {@code "a"} to {@code "b"} and {@code "c"} to {@code "b"}.
     *
     * <p>The returned map preserves the order of the entries from {@code sequence}.
     *

    Mapping<F, T> selfMapping() {
      return new Mapping<F, T>() {};
    }
  }

  public void testCyclicMapping() {
    Mapping<Integer, String> mapping = new Mapping<>();
    assertEquals(mapping.f, mapping.getFromType());
    assertEquals(mapping.t, mapping.getToType());
    assertEquals(mapping.f, mapping.flip().getFromType());
    assertEquals(mapping.t, mapping.flip().getToType());