For any subset , let denote the Banach space of restrictions to of functions . It is known that there exist bounded linear maps such that on for any . We show that can be taken to have a simple form, but cannot be taken to have an even simpler form.
Cite this article
Charles Fefferman, The Structure of Linear Extension Operators for . Rev. Mat. Iberoam. 23 (2007), no. 1, pp. 269–280