The ''portfolio effect theory'' developed by the European Commission in merger control is at the center of a fierce international row with the US authorities who believe that this theory has no economic foundations. This paper aims to provide a counter-argument and shows that full-line forcing...

A supplier is known to be subject to opportunism when contracting secretly with downstream competitors, particularly when downstream firms have "passive beliefs." We stress that in many situations, an equilibrium with passive beliefs may not exist and passive beliefs appear less plausible than...