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early 15c., assercioun, from Middle French assertion (14c.) or directly from Late Latin assertionem (nominative assertio), noun of action from past participle stem of Latin asserere "claim rights over something, state, maintain, affirm," from ad- "to" (see ad-) + serere "join" (see series). By "joining oneself" to a particular view, one "claimed" or "maintained" it.
1. An expression which, if false, indicates an error. Assertions are used for debugging by catching can't happen errors.
2. In logic programming, a new fact or rule added to the database by the program at run time. This is an extralogical or impure feature of logic programming languages.