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The arity of a CycL relation (predicate or function) is the number of arguments it takes. It is declared in the KB with the predicate #$arity.

  • Instances of #$UnaryPredicate and #$UnaryFunction take just 1 argument.
  • Instances of #$BinaryPredicate and #$BinaryFunction take 2 arguments.
  • …and so on for the other instances of #$PredicateTypeByArity

Each instance of #$VariableArityRelation is a relation that can take a variable number of arguments.