* also be called their <i>union</i>. If they are not, note that the span might contain values
   * that are not contained in either input range.
   *
   * <p>Like {@link #intersection(Range) intersection}, this operation is commutative, associative
   * and idempotent. Unlike it, it is always well-defined for any two input ranges.
   */
  public Range<C> span(Range<C> other) {

  @GwtIncompatible // java.math.BigInteger
  public void testMean() {
    // Odd-sized ranges have an obvious mean
    assertMean(2, 1, 3);

    assertMean(-2, -3, -1);
    assertMean(0, -1, 1);
    assertMean(1, -1, 3);
    assertMean((1L << 62) - 1, -1, Long.MAX_VALUE);

    // Even-sized ranges should prefer the lower mean
    assertMean(2, 1, 4);
    assertMean(-3, -4, -1);
    assertMean(0, -1, 2);

  /** The HTTP {@code User-Agent} header field name. */
  public static final String USER_AGENT = "User-Agent";

  // HTTP Response header fields

  /** The HTTP {@code Accept-Ranges} header field name. */
  public static final String ACCEPT_RANGES = "Accept-Ranges";
  /** The HTTP {@code Access-Control-Allow-Headers} header field name. */
  public static final String ACCESS_CONTROL_ALLOW_HEADERS = "Access-Control-Allow-Headers";

   * works better than Ordering.natural().nullsFirst() because, if null comes before all other
   * values, it lies outside the submap/submultiset ranges we test, and the variety of tests that
   * exercise null handling fail on those subcollections.
   */
  public abstract static class NullsBefore implements Comparator<@Nullable String>, Serializable {
    /*

import javax.annotation.CheckForNull;

/**
 * Represents an <a href="http://en.wikipedia.org/wiki/Internet_media_type">Internet Media Type</a>
 * (also known as a MIME Type or Content Type). This class also supports the concept of media ranges
 * <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1">defined by HTTP/1.1</a>.
 * As such, the {@code *} character is treated as a wildcard and is used to represent any acceptable