Nothing special about commodity exchange. The difference between marginal revenue and marginal cost is marginal wealth creation (destruction if negative). A wor

Nothing special about commodity exchange. The difference between marginal revenue and marginal cost is marginal wealth creation (destruction if negative). A world in which MR=MC is in a global maximum and no improvement is possible - any state changes imposed externally can either lead to the same score ('wealth') or make it worse. In other words, he first assumes that no improvement is possible, and then indeed manages to show that, according to the assumptions, no improvement is possible.