 A final example of the product of two modal logics (though not originally conceived as such, and presented in a slightly different way), is the Facebook Logic of Seligman, Liu, &amp; Girard (2011, 2013), useful for talking about friends and social information flow. The setting can be seen as the combination of a standard single-agent epistemic logic and a modal logic for social networks (cf. Baltag, Christoff, Rendsvig, &amp; Smets 2019; Smets &amp; Velázquez-Quesada 2017). Its semantic model consists on two domains (possible worlds W, agents \(\ttA)\) and two relations: a binary epistemic relation \({\sim_a} \subseteq (W \times W)\) for each agent \(a \in \ttA\), and a binary friendship relation \({\asymp_w} \subseteq (\ttA\times \ttA)\) for each world \(w \in W\). On the syntactic side, the language is freely generated by the standard Boolean operators and two universal modalities, K (knowledge) and \([\asymp]\) (friendship). These formulas are evaluated in pairs (world, agent), with the key clauses being the following: