We will sometimes accept new contributed environments, if the contributor shows that they add value (and not clutter).

Points that make a new environment welcome are as follows:

• It is used in a published paper, or it is a replica of an environment used in a widely known paper.

• It presents a good testbed for new methods: it's hard but not too hard; it can't be solved by well-established methods, but can be solved with recent advances.

• Code is small and clear.

• It has a solution (zoo policy) that proves the code works.