The boolean operators are:
When AND is used, all the terms in your search will appear in the returned documents, even if the terms are far apart from each other.
pensions AND social will find documents that contain both the terms pensions and social.
NB: this is the default setting, even without adding AND between terms.
Use OR when at least one of your search terms must appear in the results. You can use OR to search for synonyms, alternate spellings, or abbreviations.
pensions OR social will find documents that contain either of the terms pensions or social.
Use NOT to exclude specific terms from search results.
pensions OR social NOT tax will find documents that contain the terms pensions or social, but not the term tax.