return Collections2.safeContains(collection, element);
    }
    return Iterators.contains(iterable.iterator(), element);
  }

  /**
   * Removes, from an iterable, every element that belongs to the provided collection.
   *
   * <p>This method calls {@link Collection#removeAll} if {@code iterable} is a collection, and
   * {@link Iterators#removeAll} otherwise.
   *

 * of bugs and confusion.
 *
 * <h3>About <i>all</i> {@code Immutable-} collections</h3>
 *
 * <p>The remainder of this documentation applies to every public {@code Immutable-} type in this
 * package, whether it is a subtype of {@code ImmutableCollection} or not.
 *
 * <h4>Guarantees</h4>
 *
 * <p>Each makes the following guarantees:
 *
 * <ul>

 * of bugs and confusion.
 *
 * <h3>About <i>all</i> {@code Immutable-} collections</h3>
 *
 * <p>The remainder of this documentation applies to every public {@code Immutable-} type in this
 * package, whether it is a subtype of {@code ImmutableCollection} or not.
 *
 * <h4>Guarantees</h4>
 *
 * <p>Each makes the following guarantees:
 *
 * <ul>

   * map.
   *
   * <p>The returned map isn't threadsafe or serializable, even if {@code unfiltered} is.
   *
   * <p>Many of the filtered map's methods, such as {@code size()}, iterate across every key/value
   * mapping in the underlying map and determine which satisfy the filter. When a live view is
   * <i>not</i> needed, it may be faster to copy the filtered map and use the copy.
   *

   *       Executor)} instead, with a function that returns the next value directly.
   *   <li>Call {@link DeferredCloser#eventuallyClose(Object, Executor) closer.eventuallyClose()}
   *       for every closeable object this step creates in order to capture it for later closing.
   *   <li>Return a {@code ClosingFuture}. To turn a {@link ListenableFuture} into a {@code
   *       ClosingFuture} call {@link #from(ListenableFuture)}.

    Integer javaVersion = Ints.tryParse(JAVA_SPECIFICATION_VERSION.value());
    if (javaVersion != null && javaVersion >= 9) {
      return;
    }
    // Obviously this isn't guaranteed in every environment, but it works well enough for now:
    assertTrue(lazyStackTraceIsLazy());
  }

  @J2ktIncompatible
  @GwtIncompatible // lazyStackTrace(Throwable)
  public void testLazyStackTrace() {

    Integer javaVersion = Ints.tryParse(JAVA_SPECIFICATION_VERSION.value());
    if (javaVersion != null && javaVersion >= 9) {
      return;
    }
    // Obviously this isn't guaranteed in every environment, but it works well enough for now:
    assertTrue(lazyStackTraceIsLazy());
  }

  @J2ktIncompatible
  @GwtIncompatible // lazyStackTrace(Throwable)
  public void testLazyStackTrace() {

     * guess with an application of Newton's method, which sets guess := (guess + (x / guess)) / 2.
     * This iteration has the following two properties:
     *
     * a) every iteration (except potentially the first) has guess >= floor(sqrt(x)). This is
     * because guess' is the arithmetic mean of guess and x / guess, sqrt(x) is the geometric mean,

 */
public abstract class Converter<A, B> implements Function<A, B> {
  private final boolean handleNullAutomatically;

  // We lazily cache the reverse view to avoid allocating on every call to reverse().
  @LazyInit @RetainedWith @CheckForNull private transient Converter<B, A> reverse;

  /** Constructor for use by subclasses. */
  protected Converter() {
    this(true);
  }

   *
   * <ul>
   *   <li>A and B have equal {@link #isDirected() directedness}.
   *   <li>A and B have equal {@link #nodes() node sets}.
   *   <li>A and B have equal {@link #edges() edge sets}.
   *   <li>Every edge in A and B connects the same nodes in the same direction (if any).
   * </ul>
   *
   * <p>Network properties besides {@link #isDirected() directedness} do <b>not</b> affect equality.