Arnab Bhattacharyya is a computer scientist at the Indian Institute of Science. He returned to NCBS for the second year as a long-term visitor, and spent two months at the Simons Centre interacting with the group of Mukund Thattai as well as of other faculty members. Bhattacharyya and Thattai continued their collaborations applying methods of theoretical computer science to various biological problems. In particular, they have applied methods in graph theory to understand sets of “impossible topologies” of vesicular traffic systems, the network of transport which moves material inside eukaryotic cells. They have also started investigating the role of information exchange during sexual reproduction in eukaryotes, with the goal of identifying fundamental limits on the benefits of such exchange.