P2P systems rely on user cooperation and incentivizing cooperation is key (See also FullIncentivisation).
During my MSc thesis, I (Arman Noroozian) used the FilelistMeasurements to study properties of supply and demand of files between users and found that inside the FileList.org community there is a high probability of indirect interaction at each moment in time. Instead of uploading content to a user and expecting reciprocation in return for the provided content (TFT), indirect interaction works for example by a user "p1" providing content to a user "p2", "p2" providing content to a user "p3" and "p3" providing content to "p1" in a loop. Another example of indirect interaction is a user "p1" providing content from a file "f1" to user "p2" and expecting "p2" to reciprocate with content from a different file "f2".
The advantage of indirect interaction is that when the supply and demand of files forms a loop between the involved peers it creates incentives to upload content in the same way that TFT incentivizes users to provide content in standard BitTorrent. The difference is that with indirect interaction seeders can expect to be reciprocated for content that they seed. Studies including the FileList.org measurements show that many users download multiple files simultaneously thereby allowing such types of interactions to take place. In short indirect interaction creates seeding incentives.
--TO BE FINISHED--
Readers can refer to my thesis dissertation for more details on how indirect interaction can incentivize seeding.