Can you please provide explanation

3. In a famous article [J. viner, "Cost Curves and Supply Curves," Zeitschrift fur Nationalokonomie 3 (September 1931): 23-46], viner criticized his draftsman who could not draw a family of SAC curves whose points of tangency with the U-shaped AC curve were also the minimum points on each SAC curve. The draftsman protested that such a drawing was impossible to construct. Whom would you support in this debate