4.7 Control Predicates
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Availability:built-in
Source[ISO]\+ :Goal
True if‘Goal' cannot be proven (mnemonic: + refers to provable and the backslash (\) is normally used to indicate negation in Prolog).

Many Prolog implementations (including SWI-Prolog) provide not/1. The not/1 alternative is deprecated due to its strong link to logical negation.