The key idea is that when the government can control all consumer prices, the producer prices are independent from the consumer prices and the consumption decision part of the optimal taxation problem becomes independent of the production decision. The implication of the result is that there should be no taxes on intermediate goods and imports. Another implication is that public and private sector production should be based on the same relative prices. In practice, one needs to consider if the assumptions of the DM world are likely to apply; nevertheless, the efficiency result is a useful benchmark against which to judge whether any policy violation of production efficiency is justified.