 This definition can be extended to relations by viewing \(m\) as a code for a finite sequence in the obvious way—i.e., \(R \subseteq \mathbb{N}^k\) is c.e. just in case there is a computable function \(\phi_e(x)\) such that \(R(n_0, \ldots, n_k)\) if and only if \(\phi_e(n) = \langle n_0, \ldots, n_k \rangle\) for some \(n \in \mathbb{N}\).