Boolean logic is a system of symbolic logic used in searching databases and search engines. The core operators are AND, OR, and NOT. The AND operator is used to narrow search results by requiring that all specified terms appear in the documents returned. For example, a search for "contract AND confidential" will only return documents containing both words. Both keyword search and dtSearch in Relativity support Boolean operators.

A. ADD: This is not a standard Boolean operator; it is sometimes used in mathematical contexts but not for logical search queries.

C. JOIN: This is a command used in SQL and other database languages to combine rows from two or more tables.

D. MERGE: This is a database operation for combining datasets; it is not a Boolean search operator.

- Relativity. (n.d.). Keyword search. RelativityOne Documentation. Retrieved from https://help.relativity.com/RelativityOne/Content/Relativity/Searching/Keywordsearch.htm. (This page details the syntax for keyword searches, explicitly listing AND, OR, and NOT as supported Boolean operators).

- Relativity. (n.d.). Searching with dtSearch. RelativityOne Documentation. Retrieved from https://help.relativity.com/RelativityOne/Content/Relativity/dtSearch/SearchingwithdtSearch.htm. (This page confirms that dtSearch also supports the standard Boolean operators AND, OR, and NOT).