Embedding Finite Covering Spaces into Trivial Bundles. Vagn Lundsgaard Hansen (1978) Mathematische Annalen
Exotic Characteristic Classes and Their Relation to Universal Surgery Classes. Friedrich Hegenbarth, Artur Heil (1984) Mathematische Zeitschrift
Extension of cross-sections and a generalized de Rham theorem. Francisco Gomez (1980) Collectanea Mathematica
Extensions of symplectic groupoids and quantization. Alan Weinstein, Ping Xu (1991) Journal für die reine und angewandte Mathematik