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	/*
	* Copyright (c) 1997, 2020, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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	*/

	package java.util;

	/**
	* A collection that contains no duplicate elements. More formally, sets
	* contain no pair of elements {@code e1} and {@code e2} such that
	* {@code e1.equals(e2)}, and at most one null element. As implied by
	* its name, this interface models the mathematical <i>set</i> abstraction.
	*
	* <p>The {@code Set} interface places additional stipulations, beyond those
	* inherited from the {@code Collection} interface, on the contracts of all
	* constructors and on the contracts of the {@code add}, {@code equals} and
	* {@code hashCode} methods. Declarations for other inherited methods are
	* also included here for convenience. (The specifications accompanying these
	* declarations have been tailored to the {@code Set} interface, but they do
	* not contain any additional stipulations.)
	*
	* <p>The additional stipulation on constructors is, not surprisingly,
	* that all constructors must create a set that contains no duplicate elements
	* (as defined above).
	*
	* <p>Note: Great care must be exercised if mutable objects are used as set
	* elements. The behavior of a set is not specified if the value of an object
	* is changed in a manner that affects {@code equals} comparisons while the
	* object is an element in the set. A special case of this prohibition is
	* that it is not permissible for a set to contain itself as an element.
	*
	* <p>Some set implementations have restrictions on the elements that
	* they may contain. For example, some implementations prohibit null elements,
	* and some have restrictions on the types of their elements. Attempting to
	* add an ineligible element throws an unchecked exception, typically
	* {@code NullPointerException} or {@code ClassCastException}. Attempting
	* to query the presence of an ineligible element may throw an exception,
	* or it may simply return false; some implementations will exhibit the former
	* behavior and some will exhibit the latter. More generally, attempting an
	* operation on an ineligible element whose completion would not result in
	* the insertion of an ineligible element into the set may throw an
	* exception or it may succeed, at the option of the implementation.
	* Such exceptions are marked as "optional" in the specification for this
	* interface.
	*
	* <h2><a id="unmodifiable">Unmodifiable Sets</a></h2>
	* <p>The {@link Set#of(Object...) Set.of} and
	* {@link Set#copyOf Set.copyOf} static factory methods
	* provide a convenient way to create unmodifiable sets. The {@code Set}
	* instances created by these methods have the following characteristics:
	*
	* <ul>
	* <li>They are <a href="Collection.html#unmodifiable"><i>unmodifiable</i></a>. Elements cannot
	* be added or removed. Calling any mutator method on the Set
	* will always cause {@code UnsupportedOperationException} to be thrown.
	* However, if the contained elements are themselves mutable, this may cause the
	* Set to behave inconsistently or its contents to appear to change.
	* <li>They disallow {@code null} elements. Attempts to create them with
	* {@code null} elements result in {@code NullPointerException}.
	* <li>They are serializable if all elements are serializable.
	* <li>They reject duplicate elements at creation time. Duplicate elements
	* passed to a static factory method result in {@code IllegalArgumentException}.
	* <li>The iteration order of set elements is unspecified and is subject to change.
	* <li>They are <a href="../lang/doc-files/ValueBased.html">value-based</a>.
	* Programmers should treat instances that are {@linkplain #equals(Object) equal}
	* as interchangeable and should not use them for synchronization, or
	* unpredictable behavior may occur. For example, in a future release,
	* synchronization may fail. Callers should make no assumptions
	* about the identity of the returned instances. Factories are free to
	* create new instances or reuse existing ones.
	* <li>They are serialized as specified on the
	* <a href="{@docRoot}/serialized-form.html#java.util.CollSer">Serialized Form</a>
	* page.
	* </ul>
	*
	* <p>This interface is a member of the
	* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
	* Java Collections Framework</a>.
	*
	* @param <E> the type of elements maintained by this set
	*
	* @author Josh Bloch
	* @author Neal Gafter
	* @see Collection
	* @see List
	* @see SortedSet
	* @see HashSet
	* @see TreeSet
	* @see AbstractSet
	* @see Collections#singleton(java.lang.Object)
	* @see Collections#EMPTY_SET
	* @since 1.2
	*/

	public interface Set<E> extends Collection<E> {
	// Query Operations

	/**
	* Returns the number of elements in this set (its cardinality). If this
	* set contains more than {@code Integer.MAX_VALUE} elements, returns
	* {@code Integer.MAX_VALUE}.
	*
	* @return the number of elements in this set (its cardinality)
	*/
	int size();

	/**
	* Returns {@code true} if this set contains no elements.
	*
	* @return {@code true} if this set contains no elements
	*/
	boolean isEmpty();

	/**
	* Returns {@code true} if this set contains the specified element.
	* More formally, returns {@code true} if and only if this set
	* contains an element {@code e} such that
	* {@code Objects.equals(o, e)}.
	*
	* @param o element whose presence in this set is to be tested
	* @return {@code true} if this set contains the specified element
	* @throws ClassCastException if the type of the specified element
	* is incompatible with this set
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	* @throws NullPointerException if the specified element is null and this
	* set does not permit null elements
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	*/
	boolean contains(Object o);

	/**
	* Returns an iterator over the elements in this set. The elements are
	* returned in no particular order (unless this set is an instance of some
	* class that provides a guarantee).
	*
	* @return an iterator over the elements in this set
	*/
	Iterator<E> iterator();

	/**
	* Returns an array containing all of the elements in this set.
	* If this set makes any guarantees as to what order its elements
	* are returned by its iterator, this method must return the
	* elements in the same order.
	*
	* <p>The returned array will be "safe" in that no references to it
	* are maintained by this set. (In other words, this method must
	* allocate a new array even if this set is backed by an array).
	* The caller is thus free to modify the returned array.
	*
	* <p>This method acts as bridge between array-based and collection-based
	* APIs.
	*
	* @return an array containing all the elements in this set
	*/
	Object[] toArray();

	/**
	* Returns an array containing all of the elements in this set; the
	* runtime type of the returned array is that of the specified array.
	* If the set fits in the specified array, it is returned therein.
	* Otherwise, a new array is allocated with the runtime type of the
	* specified array and the size of this set.
	*
	* <p>If this set fits in the specified array with room to spare
	* (i.e., the array has more elements than this set), the element in
	* the array immediately following the end of the set is set to
	* {@code null}. (This is useful in determining the length of this
	* set <i>only</i> if the caller knows that this set does not contain
	* any null elements.)
	*
	* <p>If this set makes any guarantees as to what order its elements
	* are returned by its iterator, this method must return the elements
	* in the same order.
	*
	* <p>Like the {@link #toArray()} method, this method acts as bridge between
	* array-based and collection-based APIs. Further, this method allows
	* precise control over the runtime type of the output array, and may,
	* under certain circumstances, be used to save allocation costs.
	*
	* <p>Suppose {@code x} is a set known to contain only strings.
	* The following code can be used to dump the set into a newly allocated
	* array of {@code String}:
	*
	* <pre>
	* String[] y = x.toArray(new String[0]);</pre>
	*
	* Note that {@code toArray(new Object[0])} is identical in function to
	* {@code toArray()}.
	*
	* @param a the array into which the elements of this set are to be
	* stored, if it is big enough; otherwise, a new array of the same
	* runtime type is allocated for this purpose.
	* @return an array containing all the elements in this set
	* @throws ArrayStoreException if the runtime type of the specified array
	* is not a supertype of the runtime type of every element in this
	* set
	* @throws NullPointerException if the specified array is null
	*/
	<T> T[] toArray(T[] a);


	// Modification Operations

	/**
	* Adds the specified element to this set if it is not already present
	* (optional operation). More formally, adds the specified element
	* {@code e} to this set if the set contains no element {@code e2}
	* such that
	* {@code Objects.equals(e, e2)}.
	* If this set already contains the element, the call leaves the set
	* unchanged and returns {@code false}. In combination with the
	* restriction on constructors, this ensures that sets never contain
	* duplicate elements.
	*
	* <p>The stipulation above does not imply that sets must accept all
	* elements; sets may refuse to add any particular element, including
	* {@code null}, and throw an exception, as described in the
	* specification for {@link Collection#add Collection.add}.
	* Individual set implementations should clearly document any
	* restrictions on the elements that they may contain.
	*
	* @param e element to be added to this set
	* @return {@code true} if this set did not already contain the specified
	* element
	* @throws UnsupportedOperationException if the {@code add} operation
	* is not supported by this set
	* @throws ClassCastException if the class of the specified element
	* prevents it from being added to this set
	* @throws NullPointerException if the specified element is null and this
	* set does not permit null elements
	* @throws IllegalArgumentException if some property of the specified element
	* prevents it from being added to this set
	*/
	boolean add(E e);


	/**
	* Removes the specified element from this set if it is present
	* (optional operation). More formally, removes an element {@code e}
	* such that
	* {@code Objects.equals(o, e)}, if
	* this set contains such an element. Returns {@code true} if this set
	* contained the element (or equivalently, if this set changed as a
	* result of the call). (This set will not contain the element once the
	* call returns.)
	*
	* @param o object to be removed from this set, if present
	* @return {@code true} if this set contained the specified element
	* @throws ClassCastException if the type of the specified element
	* is incompatible with this set
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	* @throws NullPointerException if the specified element is null and this
	* set does not permit null elements
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	* @throws UnsupportedOperationException if the {@code remove} operation
	* is not supported by this set
	*/
	boolean remove(Object o);


	// Bulk Operations

	/**
	* Returns {@code true} if this set contains all of the elements of the
	* specified collection. If the specified collection is also a set, this
	* method returns {@code true} if it is a <i>subset</i> of this set.
	*
	* @param c collection to be checked for containment in this set
	* @return {@code true} if this set contains all of the elements of the
	* specified collection
	* @throws ClassCastException if the types of one or more elements
	* in the specified collection are incompatible with this
	* set
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	* @throws NullPointerException if the specified collection contains one
	* or more null elements and this set does not permit null
	* elements
	* (<a href="Collection.html#optional-restrictions">optional</a>),
	* or if the specified collection is null
	* @see #contains(Object)
	*/
	boolean containsAll(Collection<?> c);

	/**
	* Adds all of the elements in the specified collection to this set if
	* they're not already present (optional operation). If the specified
	* collection is also a set, the {@code addAll} operation effectively
	* modifies this set so that its value is the <i>union</i> of the two
	* sets. The behavior of this operation is undefined if the specified
	* collection is modified while the operation is in progress.
	*
	* @param c collection containing elements to be added to this set
	* @return {@code true} if this set changed as a result of the call
	*
	* @throws UnsupportedOperationException if the {@code addAll} operation
	* is not supported by this set
	* @throws ClassCastException if the class of an element of the
	* specified collection prevents it from being added to this set
	* @throws NullPointerException if the specified collection contains one
	* or more null elements and this set does not permit null
	* elements, or if the specified collection is null
	* @throws IllegalArgumentException if some property of an element of the
	* specified collection prevents it from being added to this set
	* @see #add(Object)
	*/
	boolean addAll(Collection<? extends E> c);

	/**
	* Retains only the elements in this set that are contained in the
	* specified collection (optional operation). In other words, removes
	* from this set all of its elements that are not contained in the
	* specified collection. If the specified collection is also a set, this
	* operation effectively modifies this set so that its value is the
	* <i>intersection</i> of the two sets.
	*
	* @param c collection containing elements to be retained in this set
	* @return {@code true} if this set changed as a result of the call
	* @throws UnsupportedOperationException if the {@code retainAll} operation
	* is not supported by this set
	* @throws ClassCastException if the class of an element of this set
	* is incompatible with the specified collection
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	* @throws NullPointerException if this set contains a null element and the
	* specified collection does not permit null elements
	* (<a href="Collection.html#optional-restrictions">optional</a>),
	* or if the specified collection is null
	* @see #remove(Object)
	*/
	boolean retainAll(Collection<?> c);

	/**
	* Removes from this set all of its elements that are contained in the
	* specified collection (optional operation). If the specified
	* collection is also a set, this operation effectively modifies this
	* set so that its value is the <i>asymmetric set difference</i> of
	* the two sets.
	*
	* @param c collection containing elements to be removed from this set
	* @return {@code true} if this set changed as a result of the call
	* @throws UnsupportedOperationException if the {@code removeAll} operation
	* is not supported by this set
	* @throws ClassCastException if the class of an element of this set
	* is incompatible with the specified collection
	* (<a href="Collection.html#optional-restrictions">optional</a>)
	* @throws NullPointerException if this set contains a null element and the
	* specified collection does not permit null elements
	* (<a href="Collection.html#optional-restrictions">optional</a>),
	* or if the specified collection is null
	* @see #remove(Object)
	* @see #contains(Object)
	*/
	boolean removeAll(Collection<?> c);

	/**
	* Removes all of the elements from this set (optional operation).
	* The set will be empty after this call returns.
	*
	* @throws UnsupportedOperationException if the {@code clear} method
	* is not supported by this set
	*/
	void clear();


	// Comparison and hashing

	/**
	* Compares the specified object with this set for equality. Returns
	* {@code true} if the specified object is also a set, the two sets
	* have the same size, and every member of the specified set is
	* contained in this set (or equivalently, every member of this set is
	* contained in the specified set). This definition ensures that the
	* equals method works properly across different implementations of the
	* set interface.
	*
	* @param o object to be compared for equality with this set
	* @return {@code true} if the specified object is equal to this set
	*/
	boolean equals(Object o);

	/**
	* Returns the hash code value for this set. The hash code of a set is
	* defined to be the sum of the hash codes of the elements in the set,
	* where the hash code of a {@code null} element is defined to be zero.
	* This ensures that {@code s1.equals(s2)} implies that
	* {@code s1.hashCode()==s2.hashCode()} for any two sets {@code s1}
	* and {@code s2}, as required by the general contract of
	* {@link Object#hashCode}.
	*
	* @return the hash code value for this set
	* @see Object#equals(Object)
	* @see Set#equals(Object)
	*/
	int hashCode();

	/**
	* Creates a {@code Spliterator} over the elements in this set.
	*
	* <p>The {@code Spliterator} reports {@link Spliterator#DISTINCT}.
	* Implementations should document the reporting of additional
	* characteristic values.
	*
	* @implSpec
	* The default implementation creates a
	* <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
	* from the set's {@code Iterator}. The spliterator inherits the
	* <em>fail-fast</em> properties of the set's iterator.
	* <p>
	* The created {@code Spliterator} additionally reports
	* {@link Spliterator#SIZED}.
	*
	* @implNote
	* The created {@code Spliterator} additionally reports
	* {@link Spliterator#SUBSIZED}.
	*
	* @return a {@code Spliterator} over the elements in this set
	* @since 1.8
	*/
	@Override
	default Spliterator<E> spliterator() {
	return Spliterators.spliterator(this, Spliterator.DISTINCT);
	}

	/**
	* Returns an unmodifiable set containing zero elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @return an empty {@code Set}
	*
	* @since 9
	*/
	@SuppressWarnings("unchecked")
	static <E> Set<E> of() {
	return (Set<E>) ImmutableCollections.EMPTY_SET;
	}

	/**
	* Returns an unmodifiable set containing one element.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the single element
	* @return a {@code Set} containing the specified element
	* @throws NullPointerException if the element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1) {
	return new ImmutableCollections.Set12<>(e1);
	}

	/**
	* Returns an unmodifiable set containing two elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the first element
	* @param e2 the second element
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if the elements are duplicates
	* @throws NullPointerException if an element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1, E e2) {
	return new ImmutableCollections.Set12<>(e1, e2);
	}

	/**
	* Returns an unmodifiable set containing three elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the first element
	* @param e2 the second element
	* @param e3 the third element
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if there are any duplicate elements
	* @throws NullPointerException if an element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1, E e2, E e3) {
	return new ImmutableCollections.SetN<>(e1, e2, e3);
	}

	/**
	* Returns an unmodifiable set containing four elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the first element
	* @param e2 the second element
	* @param e3 the third element
	* @param e4 the fourth element
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if there are any duplicate elements
	* @throws NullPointerException if an element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1, E e2, E e3, E e4) {
	return new ImmutableCollections.SetN<>(e1, e2, e3, e4);
	}

	/**
	* Returns an unmodifiable set containing five elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the first element
	* @param e2 the second element
	* @param e3 the third element
	* @param e4 the fourth element
	* @param e5 the fifth element
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if there are any duplicate elements
	* @throws NullPointerException if an element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5) {
	return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5);
	}

	/**
	* Returns an unmodifiable set containing six elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the first element
	* @param e2 the second element
	* @param e3 the third element
	* @param e4 the fourth element
	* @param e5 the fifth element
	* @param e6 the sixth element
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if there are any duplicate elements
	* @throws NullPointerException if an element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6) {
	return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
	e6);
	}

	/**
	* Returns an unmodifiable set containing seven elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the first element
	* @param e2 the second element
	* @param e3 the third element
	* @param e4 the fourth element
	* @param e5 the fifth element
	* @param e6 the sixth element
	* @param e7 the seventh element
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if there are any duplicate elements
	* @throws NullPointerException if an element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7) {
	return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
	e6, e7);
	}

	/**
	* Returns an unmodifiable set containing eight elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the first element
	* @param e2 the second element
	* @param e3 the third element
	* @param e4 the fourth element
	* @param e5 the fifth element
	* @param e6 the sixth element
	* @param e7 the seventh element
	* @param e8 the eighth element
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if there are any duplicate elements
	* @throws NullPointerException if an element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8) {
	return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
	e6, e7, e8);
	}

	/**
	* Returns an unmodifiable set containing nine elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the first element
	* @param e2 the second element
	* @param e3 the third element
	* @param e4 the fourth element
	* @param e5 the fifth element
	* @param e6 the sixth element
	* @param e7 the seventh element
	* @param e8 the eighth element
	* @param e9 the ninth element
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if there are any duplicate elements
	* @throws NullPointerException if an element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9) {
	return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
	e6, e7, e8, e9);
	}

	/**
	* Returns an unmodifiable set containing ten elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @param <E> the {@code Set}'s element type
	* @param e1 the first element
	* @param e2 the second element
	* @param e3 the third element
	* @param e4 the fourth element
	* @param e5 the fifth element
	* @param e6 the sixth element
	* @param e7 the seventh element
	* @param e8 the eighth element
	* @param e9 the ninth element
	* @param e10 the tenth element
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if there are any duplicate elements
	* @throws NullPointerException if an element is {@code null}
	*
	* @since 9
	*/
	static <E> Set<E> of(E e1, E e2, E e3, E e4, E e5, E e6, E e7, E e8, E e9, E e10) {
	return new ImmutableCollections.SetN<>(e1, e2, e3, e4, e5,
	e6, e7, e8, e9, e10);
	}

	/**
	* Returns an unmodifiable set containing an arbitrary number of elements.
	* See <a href="#unmodifiable">Unmodifiable Sets</a> for details.
	*
	* @apiNote
	* This method also accepts a single array as an argument. The element type of
	* the resulting set will be the component type of the array, and the size of
	* the set will be equal to the length of the array. To create a set with
	* a single element that is an array, do the following:
	*
	* <pre>{@code
	* String[] array = ... ;
	* Set<String[]> list = Set.<String[]>of(array);
	* }</pre>
	*
	* This will cause the {@link Set#of(Object) Set.of(E)} method
	* to be invoked instead.
	*
	* @param <E> the {@code Set}'s element type
	* @param elements the elements to be contained in the set
	* @return a {@code Set} containing the specified elements
	* @throws IllegalArgumentException if there are any duplicate elements
	* @throws NullPointerException if an element is {@code null} or if the array is {@code null}
	*
	* @since 9
	*/
	@SafeVarargs
	@SuppressWarnings("varargs")
	static <E> Set<E> of(E... elements) {
	switch (elements.length) { // implicit null check of elements
	case 0:
	@SuppressWarnings("unchecked")
	var set = (Set<E>) ImmutableCollections.EMPTY_SET;
	return set;
	case 1:
	return new ImmutableCollections.Set12<>(elements[0]);
	case 2:
	return new ImmutableCollections.Set12<>(elements[0], elements[1]);
	default:
	return new ImmutableCollections.SetN<>(elements);
	}
	}

	/**
	* Returns an <a href="#unmodifiable">unmodifiable Set</a> containing the elements
	* of the given Collection. The given Collection must not be null, and it must not
	* contain any null elements. If the given Collection contains duplicate elements,
	* an arbitrary element of the duplicates is preserved. If the given Collection is
	* subsequently modified, the returned Set will not reflect such modifications.
	*
	* @implNote
	* If the given Collection is an <a href="#unmodifiable">unmodifiable Set</a>,
	* calling copyOf will generally not create a copy.
	*
	* @param <E> the {@code Set}'s element type
	* @param coll a {@code Collection} from which elements are drawn, must be non-null
	* @return a {@code Set} containing the elements of the given {@code Collection}
	* @throws NullPointerException if coll is null, or if it contains any nulls
	* @since 10
	*/
	@SuppressWarnings("unchecked")
	static <E> Set<E> copyOf(Collection<? extends E> coll) {
	if (coll instanceof ImmutableCollections.AbstractImmutableSet) {
	return (Set<E>)coll;
	} else {
	return (Set<E>)Set.of(new HashSet<>(coll).toArray());
	}
	}
	}

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