This book is both available in https://distsn.gitbook.io/recommendation-fairness and https://github.com/hakaba-hitoyo/gitbook-decentralization.
In the internet, especially in the user-generated content platforms, the presence of users is oligopolized by few celebrities. I propose the term internet of celebrities. On the other hand, Mastodon and other federated social networks share the philosophy of decentralization. Usually they imagine that some federated instances share the power of their social network, actually the decentralization of users is also motivated. The decentralization of users is the counterpart of the internet of celebrities.
A list of users which is ordered by the number of followers is a typical example of the design which supports the oligarchy of the users. Although the users who have many followers are likely to be attractive, it is unfair that the users who are not famous are rarely featured.
I also propose the term recommendation fairness, or just fairness for short, in this book which means to support the decentralization of users. By contrast, unfairness means to support the oligarchy of users. In this book, many websites are evaluated by their fairness and unfairness, especially the user recommendation systems for Mastodon.