In a logical calculus, a signature \(\Sigma\) is a triple \((V_\Sigma,F_\Sigma,P_\Sigma)\) of the following sets:
Every function \(f\in F_\Sigma\) has an arity $n\ge 0$, while for $n=0$ we call the functions constants.
Every predicate \(p\in P_\Sigma\) has an arity \(n\ge 1\).
