The Union option is used to combine the terms from one or more highlighted sets with the OR operator. This is useful when you want to refine your search results to include the terms used in Set1 OR Set2 OR Set3, for however many sets you highlight. Highlight Set 3 as well as Set 4 in the Search History box. Click Union . Union is merely another option of combining terms without having to retype them.
Common limits are for a specific language, such as English, or for records with abstracts.
When limits are available, they are displayed after the search options in the form of check boxes. Click the check boxes Human and English , as shown below. Click Narrow . The Search History box updates with a new set of records.