SWI-Prolog -- (\+)/1

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Predicate \+/1

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  - Built-in Predicates
    - Control Predicates
      - fail/0
      - false/0
      - true/0
      - repeat/0
      - !/0
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      - \+/1
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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.