- Open the database
**Hopf_ring_nets**and compute the adjacency matrices for the crystal structure (default parameters for AutoCN). - Build standard representation for the record GULBAR. Be sure that the resulting simplified net consists
of 4-coordinated Zn atoms.
__(do not forget to remove 2-c nodes by means of the Simplify Adjacency Matrix procedure)__ - For the simplified structure run ADS in the
**Ring Net**simplification mode with the following options specified (remember to select all atoms as “central atoms”):

- Open
**Crystal Data**window for the simplified structure and be sure that there are six links marked as "**H bonds**" per each ring center (node of the ring net).

Using the ADS classification mode (see Module 5) you may determine the topology of the Hopf ring net (the net of H bonds) as 6-c**hxg**. (Tip: set in**Topology/Bond Types**: H-bonds:**At.**/ Valence:**None**)

** Exercise:** simplify another structure in the

For more details on Hopf Ring Nets see “A topological method for classification of entanglements in crystal
networks” E. V. Alexandrov, V. A. Blatov and D. M. Proserpio, *Acta Cryst*., **A68**, 2012, 484-493.