public ImmutableSortedMap<K, V> subMap(
      K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
    checkNotNull(fromKey);
    checkNotNull(toKey);
    checkArgument(
        comparator().compare(fromKey, toKey) <= 0,
        "expected fromKey <= toKey but %s > %s",
        fromKey,
        toKey);
    return headMap(toKey, toInclusive).tailMap(fromKey, fromInclusive);
  }

  /**

  }

  @Override
  public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
    return new SafeTreeMap<>(
        delegate.subMap(checkValid(fromKey), fromInclusive, checkValid(toKey), toInclusive));
  }

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

  @Override

  }

  public ImmutableSortedMap<K, V> subMap(K fromKey, K toKey) {
    checkNotNull(fromKey);
    checkNotNull(toKey);
    checkArgument(comparator.compare(fromKey, toKey) <= 0);
    return newView(sortedDelegate.subMap(fromKey, toKey));
  }

  ImmutableSortedMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
    checkNotNull(fromKey);
    checkNotNull(toKey);

  }

  @Override
  public NavigableMap<K, V> subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
    return new SafeTreeMap<>(
        delegate.subMap(checkValid(fromKey), fromInclusive, checkValid(toKey), toInclusive));
  }

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

  @Override

    @Override
    public NavigableMap<K, V> subMap(
        K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate().subMap(fromKey, fromInclusive, toKey, toInclusive);
    }

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

    @Override

  public ImmutableSortedMap<K, V> subMap(
      K fromKey, boolean fromInclusive, K toKey, boolean toInclusive) {
    checkNotNull(fromKey);
    checkNotNull(toKey);
    checkArgument(
        comparator().compare(fromKey, toKey) <= 0,
        "expected fromKey <= toKey but %s > %s",
        fromKey,
        toKey);
    return headMap(toKey, toInclusive).tailMap(fromKey, fromInclusive);
  }

  /**

          && (upperBound == null || compare(upperBound, o) > 0);
    }

    @Override
    public SortedMap<C, V> subMap(C fromKey, C toKey) {
      checkArgument(rangeContains(checkNotNull(fromKey)) && rangeContains(checkNotNull(toKey)));
      return new TreeRow(rowKey, fromKey, toKey);
    }

    @Override
    public SortedMap<C, V> headMap(C toKey) {
      checkArgument(rangeContains(checkNotNull(toKey)));

    }

    @Override
    public SortedMap<K, V2> subMap(@ParametricNullness K fromKey, @ParametricNullness K toKey) {
      return transformEntries(fromMap().subMap(fromKey, toKey), transformer);
    }

    @Override
    public SortedMap<K, V2> tailMap(@ParametricNullness K fromKey) {
      return transformEntries(fromMap().tailMap(fromKey), transformer);
    }
  }

  @GwtIncompatible // NavigableMap

    }

    @Override
    public SortedMap<K, V2> subMap(@ParametricNullness K fromKey, @ParametricNullness K toKey) {
      return transformEntries(fromMap().subMap(fromKey, toKey), transformer);
    }

    @Override
    public SortedMap<K, V2> tailMap(@ParametricNullness K fromKey) {
      return transformEntries(fromMap().tailMap(fromKey), transformer);
    }
  }

  @GwtIncompatible // NavigableMap

    }

    @Override
    public SortedMap<K, V> subMap(K fromKey, K toKey) {
      synchronized (mutex) {
        return sortedMap(delegate().subMap(fromKey, toKey), mutex);
      }
    }

    @Override
    public SortedMap<K, V> tailMap(K fromKey) {
      synchronized (mutex) {
        return sortedMap(delegate().tailMap(fromKey), mutex);
      }
    }