  This is a variation of the two-sided market model of [10]: Demand D is
concave in \tilde{D} in (16) of [10] So, in (5) of [10] and after Theorem 2,
take the parametric case 0 < a <1. Thus, demand D is both decreasing and
concave in price p, and so the utilities (U=pD) are also concave in price.
Also, herein a simpler illustrative demand-response model is used in Appendix A
and B.
