Consider a node \(n_{i}\), then \(U_{1}\) is the set of nodes \(n_{j}\) such that \(D(n_{i}, n_{j}) = 1\), i.e., \(U_{1}\) brings together the closest neighbours of \(n_{i}\). Likewise, we can define \(U_{2}\) as the set of nodes \(n_{k}\) such that \(D(n_{i}, n_{k})\) is at most 2. It follows that \(U_{n} \subseteq U_{n+1}\) and so we obtain a nested series of neighbourhoods of \(n_{i}\). If one understands dimension as a measure of the “growth” of the neighbourhoods, then dimension can be defined as: