We introduce the notion of -numbers for operators in Banach couples. We investigate variants of the approximation, Gelfand, and Kolmogorov numbers. In particular, we derive upper estimates of these numbers for operators between spaces generated by interpolation functors on Banach couples satisfying interpolation variants of approximation properties. We also study two-sided interpolation of entropy numbers.
"Interpolation of -numbers and entropy numbers of operators." Banach J. Math. Anal. 13 (2) 427 - 448, April 2019. https://doi.org/10.1215/17358787-2018-0046