 Recall that from this point on in PM, the relations are to be considered as “relations in extension” and so it is easy to see how one can treat the relations as ordered \(n+1\)-tuples of which the last member is unique given the first n arguments. In particular, a monadic function f can be seen in the familiar way as a set of ordered pairs (of \(\langle x, f_R(x) \rangle\)) for each argument x in the domain of the function.