* This method returns a {@code ImmutableSortedMap}, consisting of the entries whose keys ranges
   * from {@code fromKey}, inclusive, to {@code toKey}, exclusive.
   *
   * <p>The {@link SortedMap#subMap} documentation states that a submap of a submap throws an {@link
   * IllegalArgumentException} if passed a {@code fromKey} less than an earlier {@code fromKey}.
   * However, this method doesn't throw an exception in that situation, but instead keeps the

    return Maps.keyOrNull(higherEntry(key));
  }

  abstract Iterator<Entry<K, V>> descendingEntryIterator();

  @Override
  public SortedMap<K, V> subMap(@ParametricNullness K fromKey, @ParametricNullness K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  @Override
  public SortedMap<K, V> headMap(@ParametricNullness K toKey) {
    return headMap(toKey, false);
  }

  @Override

    table.put("b", "b", "x");
    table.put("b", "c", "y");
    table.put("b", "x", "n");
    table.put("a", "a", "d");
    table.row("b").subMap("c", "x").clear();
    assertEquals(table.row("b"), ImmutableMap.of("b", "x", "x", "n"));
    table.row("b").subMap("b", "y").clear();
    assertEquals(table.row("b"), ImmutableMap.of());
    assertFalse(table.backingMap.containsKey("b"));
  }

    return Maps.keyOrNull(higherEntry(key));
  }

  abstract Iterator<Entry<K, V>> descendingEntryIterator();

  @Override
  public SortedMap<K, V> subMap(@ParametricNullness K fromKey, @ParametricNullness K toKey) {
    return subMap(fromKey, true, toKey, false);
  }

  @Override
  public SortedMap<K, V> headMap(@ParametricNullness K toKey) {
    return headMap(toKey, false);
  }

  @Override

        assertEqualInOrder(
            entries.subList(i, j),
            navigableMap.subMap(entries.get(i).getKey(), entries.get(j).getKey()).entrySet());
      }
    }
  }

  @CollectionSize.Require(SEVERAL)
  public void testSubMapIllegal() {
    assertThrows(IllegalArgumentException.class, () -> navigableMap.subMap(c.getKey(), a.getKey()));
  }

  @CollectionSize.Require(absent = ZERO)

          .rowMap();
    }

    @Override
    public SortedMap<R, Map<C, V>> subMap(R fromKey, R toKey) {
      checkNotNull(fromKey);
      checkNotNull(toKey);
      return new StandardRowSortedTable<R, C, V>(sortedBackingMap().subMap(fromKey, toKey), factory)
          .rowMap();
    }

    @Override
    public SortedMap<R, Map<C, V>> tailMap(R fromKey) {

          .rowMap();
    }

    @Override
    public SortedMap<R, Map<C, V>> subMap(R fromKey, R toKey) {
      checkNotNull(fromKey);
      checkNotNull(toKey);
      return new StandardRowSortedTable<R, C, V>(sortedBackingMap().subMap(fromKey, toKey), factory)
          .rowMap();
    }

    @Override
    public SortedMap<R, Map<C, V>> tailMap(R fromKey) {

    Set<Feature<?>> keySetFeatures = computeCommonDerivedCollectionFeatures(mapFeatures);

    // TODO(lowasser): make this trigger only if the map is a submap
    // currently, the KeySetGenerator won't work properly for a subset of a keyset of a submap
    keySetFeatures.add(CollectionFeature.SUBSET_VIEW);
    if (mapFeatures.contains(MapFeature.ALLOWS_NULL_KEYS)) {
      keySetFeatures.add(CollectionFeature.ALLOWS_NULL_VALUES);

    }

    @Override
    public Entry<K, V>[] createArray(int length) {
      return delegate.createArray(length);
    }
  }

  /** Two bounds (from and to) define how to build a subMap. */
  public enum Bound {
    INCLUSIVE,
    EXCLUSIVE,
    NO_BOUND;
  }

  public static class SortedSetSubsetTestSetGenerator<E extends @Nullable Object>
      implements TestSortedSetGenerator<E> {

        assertEqualInOrder(
            entries.subList(i, j),
            navigableMap.subMap(entries.get(i).getKey(), entries.get(j).getKey()).entrySet());
      }
    }
  }

  @CollectionSize.Require(SEVERAL)
  public void testSubMapIllegal() {
    assertThrows(IllegalArgumentException.class, () -> navigableMap.subMap(c.getKey(), a.getKey()));
  }

  @CollectionSize.Require(absent = ZERO)