Optimal redistricting under geographical constraints: Why "pack and crack" does not work

We show that optimal partisan redistricting with geographical constraints is a computationally intractable (NP-complete) problem. In particular, even when voter's preferences are deterministic, a solution is generally not obtained by concentrating opponent's supporters in \unwinnable" districts ("packing") and spreading one's own supporters evenly among the other districts in order to produce many slight marginal wins ("cracking").

Vertikális korlátozások - növelik vagy csökkentik a jólétet? Érvek az irodalomból = Vertical constraints - do they increase or reduce welfare? Arguments in the literature

A vertikális korlátozások témaköre a versenypolitika és -szabályozás egyik legfontosabb, de mindenképpen legtöbb vitát generáló területe. A téma magyar irodalma elsősorban elméleti kérdésekkel foglalkozik, mellőzve a konkrét iránymutatásokat a probléma kezelésére. Először röviden bemutatjuk a vertikális korlátozások indokait és hatásmechanizmusát magyarázó teoretikus irodalmat, felsorolva azok hatékonyságnövelő hatását hangsúlyozó érvrendszereket, illetve a versenykorlátozás lehetőségét tárgyaló modelleket is. Ezután bemutatjuk, hogy milyen fontos empirikus vizsgálatokat végeztek ezen elméletek vizsgálatára, és milyen következtetések vonhatóak le a tapasztalatokból. _________ The field of vertical constraints is one of the most important in competition policy and regulation, but one that generates the most debate. Hungarian literature on the subject deals primarily with theoretical questions, refraining from offering specific guidelines for handling the problem. The paper first covers briefly the causes of the vertical constraints and the Hungarian theoretical literature on its effective mechanism, listing the system of arguments that point to its effect of increasing efficiency and the models that discuss the possibility of limiting competition. The paper then presents the major empirical examinations made of these theories and the conclusions drawn from that experience.

Hedging under liquidity constraints

Although risk management can be justified by financial distress, the theoretical models usually contain hedging instruments free of funding risk. In practice, management of the counterparty risk in derivative transactions is of enhanced importance, consequently not only is trading on exchanges subject to the presence of a margin account, but also in bilateral (OTC) agreements parties will require margins or collateral from their partners in order to hedge the mark-tomarket loss of the transaction. The aim of this paper is to present and compare two models where the financing need of the hedging instrument also appears, influencing the hedging strategy and the optimal hedging ratio. Both models contain the same source of risk and optimisation criterion, but the liquidity risk is modelled in different ways. In the first model, there is no additional financing resource that can be used to finance the margin account in case of a margin call, which entails the risk of liquidation of the hedging position. In the second model, the financing is available but a given credit spread is to be paid for this, so hedging can become costly.