Some implementations of logic, notably Prolog apply negation as failure, which means that if a solution is not found (failure), the thing you are trying to solve is deemed as not true (negation). This effectvely adopts the closed world assumption - if raw facts are not explciitly stated they are false, or in other words all facts are known in the knowledge base.
Used in Chap. 2: page 16; Chap. 17: page 253
Used in glossary entries: closed world assumption, knowledge base, Prolog