operators between normed spaces
This paper will give a brief survey of ideas related to 'elements of finite closed descent' in certain kinds of topological algebra.
An error in the paper named in the title ibid., 42-4 (1992)875-889 is corrected.
A gap in the proof of [4, Theorem 1] is removed.
The position of intermediate spaces for a Banach couple is estimated with the help of its fundamental function and co-function. We study the completeness of the collection of all such functions, and the methods of calculating and estimating them for different couples. Finally, these functions are used to compare the position of spaces obtained under the action of some interpolation functors.