The Refine your results section, which appears on the left side of the Brief Results page, contains a list of categories, which are referred to as facets. To obtain the desired search results, you can refine your search by selecting or deselecting specific facets such as date, author, and record type. Additionally, you have the option to filter your results to include only peer-reviewed journal articles or books available in the NU Library.
When facets are added one at a time, the system returns the remaining results that match the selected facet value. You can specify more complex filtering if you select multiple facets and then apply them to the results at the same time.
For example, if you select Subject facet values Agriculture and Botany and Resource Type facet values Book and Other, the system returns results that include all records that match the following criteria:
The records must contain either Agriculture or Botany subjects.
And the records must be either Book or Other resource types.
If you had selected these facet values separately, the resulting records would have to contain all of these facet values.
To include/exclude multiple facets at a time:
Include facet – Select the checkbox on the left side of the facet. If you want to include a facet that has already been marked for exclusion, select the 
button on the right side of the facet.
Exclude facet – If you have already included a facet, select the 
button on the right side of the facet to mark it for exclusion. If you have not already marked a facet for exclusion or inclusion, you must first select the facet's checkbox and select the button on the right side of the facet. Otherwise, a single facet is excluded immediately.
When performing many similar types of searches, you may want to retain your filters for subsequent searches within a search session.
To make a facet persistent, hover the cursor over the facet in the Active Filters section and then select the facet's padlock 
To remove a facet's persistence, click the facet's padlock or delete the facet.
Read more: Filtering search results in Primo