similarly other more sophisticated versions are available for surfacewater groundwater interactions such as partially penetrating wells or streambed clogging eg hunt hunt the lagrange multiplier a may then be interpreted as the effective present value entitlement price if the marginal damage of the externality is equivalent for all firms this outcome can be induced with marketable entitlements that are traded on a onetoone basis where marginal abatement costs of all firms will equal marginal damage multiplied by a kuwayama and brozovid palazzo and brozovic