A very useful notion in topology is the notion of a proper map, which is the relative notion of compactness. For instance, a continuous family of compact cycles \((X_s)_{s \in S}\) in a given complex space M, parameterized by a Hausdorff topological space S, is proper if and only if the set-theoretical graph, \(\displaystyle |G| := \{(s,x) \in S \times M \ / \ x \in |X_s| \} \) is proper over S.