static <E extends @Nullable Object> Sets.SetView<E> | 
Sets.difference(Set<E> set1,
          Set<?> set2) | 
 Returns an unmodifiable view of the difference of two sets. 
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static <E extends @Nullable Object> Sets.SetView<E> | 
Sets.intersection(Set<E> set1,
            Set<?> set2) | 
 Returns an unmodifiable view of the intersection of two sets. 
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static <E extends @Nullable Object> Sets.SetView<E> | 
Sets.symmetricDifference(Set<? extends E> set1,
                   Set<? extends E> set2) | 
 Returns an unmodifiable view of the symmetric difference of two sets. 
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static <E extends @Nullable Object> Sets.SetView<E> | 
Sets.union(Set<? extends E> set1,
     Set<? extends E> set2) | 
 Returns an unmodifiable view of the union of two sets. 
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