Predicate symbol
= Predicate symbol
{title2=$P^{(k)}$}
A <predicate symbol> of arity $k$ is interpreted as a subset of the $k$th Cartesian power of a structure's domain. Applying it to $k$ <first-order terms> gives an <atomic formula>. In a singleton domain there is only one possible argument tuple at each arity, but a predicate may still be interpreted as either the empty relation or the full relation.