Media firms sometimes allow consumers to pay to remove advertisements from an advertisement-based product. We formally examine an ad-based monopolist's incentives to introduce this option. When deciding whether to introduce the option to pay, the monopolist compares the potential direct revenues...

We survey the literature on social networks by putting together the economics, sociological and physics/applied mathematics approaches, showing their similarities and differences. We expose, in particular, the two main ways of modeling network formation. While the physics/applied mathematics...