PaperChain

The `PaperChain' representation finds all rings up to a user-defined maximum size by walking the molecular topology, then proceeds to render each ring by fitting a polyhedron to the involved atoms and the ring centroid. The rings are drawn as bipyramids with a user-controlled height. The rings are colored by pucker, using the Cremer-Pople pucker amplitude, which is defined for all rings of three atoms or greater.