When you are building more complex searches, it is useful to combine searches in your search history. In ProQuest, those searches can be found under Recent Searches.
Recent Searches can be accessed on the Advanced Search page and the most recent Search Results page:

Once you have clicked on the Recent Searches link, you will find all the searches you have conducted during your session listed beside a search number. You can immediately use those numbers to work with the searches.
Combine search numbers using Boolean operators to make more complex searches without re-writing anything: 1 AND 2, (3 OR 4) AND 8, and so on:
