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

    private static final long serialVersionUID = 0;
  }

  @GwtIncompatible // works but is needed only for NavigableMap
  @CheckForNull
  private static <K extends @Nullable Object, V extends @Nullable Object>
      Map.Entry<K, V> nullableSynchronizedEntry(

          assertTrue(left + " should be after " + right, i >= j);
        }
        j++;
      }
      i++;
    }
  }

  // Tests to make sure assertSubtypeBeforeSupertype() works.

  public void testAssertSubtypeTokenBeforeSupertypeToken_empty() {
    assertSubtypeTokenBeforeSupertypeToken(ImmutableList.<TypeToken<?>>of());
  }

     * performed at the front of each bin. This makes it easy to check changes, and also fast to
     * traverse. When nodes would otherwise be changed, new nodes are created to replace them. This
     * works well for hash tables since the bin lists tend to be short. (The average length is less
     * than two.)
     *
     * Read operations can thus proceed without locking, but rely on selected uses of volatiles to

      // Warning: this is broken if size() == 0, so it is critical that we
      // substitute an empty ImmutableSet to the user in place of this

      // It's a weird formula, but tests prove it works.
      int adjust = size() - 1;
      for (int i = 0; i < axes.size(); i++) {
        adjust *= 31;
        adjust = ~~adjust;
        // in GWT, we have to deal with integer overflow carefully
      }

          assertTrue(left + " should be after " + right, i >= j);
        }
        j++;
      }
      i++;
    }
  }

  // Tests to make sure assertSubtypeBeforeSupertype() works.

  public void testAssertSubtypeTokenBeforeSupertypeToken_empty() {
    assertSubtypeTokenBeforeSupertypeToken(ImmutableList.<TypeToken<?>>of());
  }