*
 * <p>The classes in this package include:
 *
 * <h2>Immutable collections</h2>
 *
 * These are collections whose contents will never change. They also offer a few additional
 * guarantees (see {@link ImmutableCollection} for details). Implementations are available for both
 * the JDK collection types and the Guava collection types (listed below).
 *

   * In JDK 1.7.0_51-b13, {@link TypeVariableImpl#equals(Object)} is changed to no longer be equal
   * to custom TypeVariable implementations. As a result, we need to make sure our TypeVariable
   * implementation respects symmetry. Moreover, we don't want to reconstruct a native type variable
   * {@code <A>} using our implementation unless some of its bounds have changed in resolution. This

 *
 * <p><b>Warning:</b> The methods of {@code ForwardingSortedMultiset} forward
 * <b>indiscriminately</b> to the methods of the delegate. For example, overriding {@link
 * #add(Object, int)} alone <b>will not</b> change the behavior of {@link #add(Object)}, which can
 * lead to unexpected behavior. In this case, you should override {@code add(Object)} as well,
 * either providing your own implementation, or delegating to the provided {@code standardAdd}

  /**
   * Verifies that a collection is immutable.
   *
   * <p>A collection is considered immutable if:
   *
   * <ol>
   *   <li>All its mutation methods result in UnsupportedOperationException, and do not change the
   *       underlying contents.
   *   <li>All methods that return objects that can indirectly mutate the collection throw
   *       UnsupportedOperationException when those mutators are called.
   * </ol>
   *

  /**
   * Verify thread safety by using a collection whose size() may be inconsistent with the actual
   * number of elements and whose elements may change over time.
   *
   * <p>This test might fail in GWT because the GWT emulations might count on the input collection
   * not to change during the copy. It is safe to do so in GWT because javascript is
   * single-threaded.
   */
  @GwtIncompatible // GWT is single threaded

  /**
   * Verify thread safety by using a collection whose size() may be inconsistent with the actual
   * number of elements and whose elements may change over time.
   *
   * <p>This test might fail in GWT because the GWT emulations might count on the input collection
   * not to change during the copy. It is safe to do so in GWT because javascript is
   * single-threaded.
   */
  @GwtIncompatible // GWT is single threaded

import java.util.function.ToIntFunction;
import java.util.stream.Collector;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * A {@link Multiset} whose contents will never change, with many other important properties
 * detailed at {@link ImmutableCollection}.
 *
 * <p><b>Grouped iteration.</b> In all current implementations, duplicate elements always appear

            return false;
          }
        }
        return true;
      } catch (ClassCastException e) {
        return false;
      } catch (NoSuchElementException e) {
        return false; // concurrent change to other set
      }
    }
    return containsAll(that);
  }

  @Override
  public E first() {
    if (isEmpty()) {
      throw new NoSuchElementException();
    }

   * as the {@link #elementSet}). The order of the elements in the element set is unspecified.
   *
   * <p>The entry set is backed by the same data as the multiset, so any change to either is
   * immediately reflected in the other. However, multiset changes may or may not be reflected in
   * any {@code Entry} instances already retrieved from the entry set (this is

 *
 * <p><b>Warning:</b> The methods of {@code ForwardingList} forward <b>indiscriminately</b> to the
 * methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the
 * behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
 * override {@code addAll} as well, either providing your own implementation, or delegating to the