/** The Greek letter delta, used in unicode testing. */
  private static final String DELTA = "\u0394";

  /** A domain part which is valid under lenient validation, but invalid under strict validation. */
  static final String LOTS_OF_DELTAS = Strings.repeat(DELTA, 62);

  private static final String ALMOST_TOO_MANY_LEVELS = Strings.repeat("a.", 127);

    private final ImmutableIntArray parent;

    private AsList(ImmutableIntArray parent) {
      this.parent = parent;
    }

    // inherit: isEmpty, containsAll, toArray x2, {,list,spl}iterator, stream, forEach, mutations

    @Override
    public int size() {
      return parent.length();
    }

    @Override
    public Integer get(int index) {
      return parent.get(index);
    }

 *   for (Runnable task : tasks) {
 *     rateLimiter.acquire(); // may wait
 *     executor.execute(task);
 *   }
 * }
 * }</pre>
 *
 * <p>As another example, imagine that we produce a stream of data, and we want to cap it at 5kb per
 * second. This could be accomplished by requiring a permit per byte, and specifying a rate of 5000
 * permits per second:
 *
 * <pre>{@code

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.NavigableSet;
import java.util.SortedSet;
import java.util.stream.Collector;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A {@link NavigableSet} whose contents will never change, with many other important properties

         * halfSquare. (We have to deal with overflow, though.)
         *
         * If we treat halfSquare as an unsigned long, we know that
         *            sqrtFloor^2 <= x < (sqrtFloor + 1)^2
         * halfSquare - sqrtFloor <= x < halfSquare + sqrtFloor + 1
         * so |x - halfSquare| <= sqrtFloor.  Therefore, it's safe to treat x - halfSquare as a
         * signed long, so lessThanBranchFree is safe for use.
         */

  static final double MEGA_STREAM_MIN = 0.0;
  static final double MEGA_STREAM_MAX = MEGA_STREAM_COUNT - 1;
  static final double MEGA_STREAM_MEAN = MEGA_STREAM_MAX / 2;
  static final double MEGA_STREAM_POPULATION_VARIANCE =
      (MEGA_STREAM_COUNT - 1) * (MEGA_STREAM_COUNT + 1) / 12.0;

  // Stats instances:

  static final Stats EMPTY_STATS_VARARGS = Stats.of();

   * offset that is greater than the current length of the source, a stream is then opened to that
   * source, and finally additional bytes are appended to the source before the stream is read.
   *
   * <p>Without special handling, it's possible to have reads of the open stream start <i>before</i>
   * the offset at which the slice is supposed to start.
   */

    @J2ktIncompatible
    private void writeObject(ObjectOutputStream stream) throws IOException {
      stream.defaultWriteObject();
      stream.writeObject(inverse());
    }

    @GwtIncompatible // java.io.ObjectInputStream
    @J2ktIncompatible
    @SuppressWarnings("unchecked") // reading data stored by writeObject
    private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {

  private void writeObject(ObjectOutputStream stream) throws IOException {
    stream.defaultWriteObject();
    stream.writeObject(countMap);
  }

  @J2ktIncompatible // serialization
  private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
    stream.defaultReadObject();
    @SuppressWarnings("unchecked") // reading data stored by writeObject

   * <p><b>Comparison to {@code java.util.Optional}:</b> this method has no equivalent in Java 8's
   * {@code Optional} class; use {@code
   * optionals.stream().filter(Optional::isPresent).map(Optional::get)} instead.
   *
   * <p><b>Java 9 users:</b> use {@code optionals.stream().flatMap(Optional::stream)} instead.
   *
   * @since 11.0 (generics widened in 13.0)
   */
  public static <T> Iterable<T> presentInstances(