Step (i) deserves special consideration. It consists in building a new unit cell from the set of positive translations t of the edges, positive in the sense of being lexicographically greater than 0 3 . Negative translations are negated to only keep positive ones. By construction, this set (b) Represent the graph in the basis given by the candidate (the former unit cell and two of its neighbours are represented in orange). Note that axes x and y are now orthogonal.