The embedding functions of an intermediate space into a Banach couple are defined as its embedding constants into the couples , . Using these functions, we study properties and interrelations of different intermediate spaces, give a new description of all real interpolation spaces, and generalize the concept of weak-type interpolation to any Banach couple to obtain new interpolation theorems.
"Embedding functions and their role in interpolation theory." Abstr. Appl. Anal. 1 (3) 305 - 325, 1996. https://doi.org/10.1155/S1085337596000164