Professor David Edmunds is Emeritus Professor of the Mathematics, Analysis and Partial Differential Equations Research Group at University of Sussex. His main research interests are functional analysis, interpolation theory, the theory of function spaces, sharp estimates of s-numbers and entropy numbers of embeddings and classical operators, and elliptic partial differential equations. He was awarded the LMS Polya prize in 1996, the Czech Academy of Sciences Bolzano prize in 1998, and was elected to a fellowship of the Learned Society of Wales in 2012.; Professor Des Evans of Emeritus Professor of Mathematics at Cardiff University. His main research interests are in the spectral theory associated with differential equations and related areas of analysis and quantum mechanics. I was elected to a Fellowship of the Learned Society of Wales in 2010.