EvaluatableRelation #$TruthFunction #$FixedArityRelation #$PartiallyCommutativeRelation</p>
<p>#$arity   arity (intangible object relating predicate) (default monotonic predicate) (predicate that is functional in its second argument)</p>
<p>    A #$MetaRelation used for stating that a given relation takes a specified number of arguments. (#$arity RELN N) means that that semantic well-formedness requires that RELN take exactly N arguments at a time. That is, a formula (RELN ARG1 ... ARGM) is semanticall