Arc facets construction:(a) Examples of arc facets patterns. In the first and the second examples, the Fin indexes have been swapped. In the third example, the Fin root facets have been fused on a single one. The last example shows root F out facets lying on a non-convex contour. As for the ORF rings, facets in each arc are ordered either at the level of individual arcs or across the whole sequence of arcs as illustrated in the third row. (b) The number of facets across the arcs follows an arithmetic progression.