Suppose that chemicals from a mining site pollute a nearby lake, which also happens to be used by a fishery to raise fish. The marginal damage from chemical emissions to the fishery is given by MD = 2E. The marginal abatement cost to the mining company factory is given by MAC = 90 - 3E. An environmental dispute arises; and, as a settlement of the environmental dispute, the fishery is given the right to use the lake.