When there are no transaction costs, but in the presence of
externalities (e.g., pollution), under what circumstances is the
equilibrium allocation of physical resources, including the
equilibrium level of externalities, independent of the assignment
of rights and liabilities to different agents? Under what
circumstances will an efficient equilibrium allocation necessarily
result? What is the role for law, if any, in improving the outcome
of private negotiations between private parties engaged in
activities that have external effects