Nonjoint production and the cost function: Some refinements (Q1079101)

\textit{R. E. Hall} [J. Polit. Econ. 81, 878-892 (1973)] gives characterizations of a nonjoint technology in terms of the technology's input requirement sets and in terms of its cost functions. Hall's theorems are reconsidered and an improvement is obtained in the formulations. It is shown that a restatement is needed, especially, with respect to the cost function theorem, in order to avoid misunderstandings. Furthermore, a local version of nonjoint production is formulated.