Consider a social network, comprising individuals linked to each other according to a relation BFF. In particular, access to postings is based on BFF, as follows: If hI, I0 i BFF holds then individual I is authorized to read postings by individual I 0 . Goals that might constrain BFF as it applies to a given individual I could include (i) restrict which individuals can read postings by I, and (ii) restrict which individuals postings I can read.

(a) Give a plausible situation where goal (i) is useful.

(b) Give a plausible situation where goal (ii) is useful.

(c) To what extent do (i) and/or (ii) become more difficult to preserve if the BFF relation is symmetric and/or it is transitive.