Figure : Continued: Illustration of the algorithm used to extract a key from a candidate on a 2-dimensional graph does not depend on the previous representation of the graph, it only depends on the candidate. As a consequence, any deterministic algorithm that transforms a set of translations into a unit cell can be used for this purpose. Delgado-Friedrichs and O'Keeffe mention this point and suggest triangulating the translations, without detailing their algorithm. Before presenting the one used here, let's sketch the general idea and prove a lemma.