When economist Jacob Viner first developed the envelope relationship, he told his draftsman to make sure that all the marginal cost curves went through both

(1) the minimum point of the short-run average cost curve and (2) the point where the short-run average total cost curve was tangent to the long-run average total cost curve. The draftsman told him it couldn’t be done. Viner told him to do it anyhow. Why was the draftsman right?