@article{700999,
     title = {Entropy numbers of operators in Banach spaces},
     booktitle = {General topology and its relations to modern analysis and algebra IV},
     series = {GDML\_Books},
     publisher = {Springer},
     address = {Berlin},
     year = {1977},
     pages = {[21]-33},
     mrnumber = {MR0458217},
     zbl = {0361.47015},
     url = {http://dml.mathdoc.fr/item/700999}
}

Carl, B.; Pietsch, A. Entropy numbers of operators in Banach spaces, dans General topology and its relations to modern analysis and algebra IV, GDML_Books,  (1977), pp. [21]-33. http://gdmltest.u-ga.fr/item/700999/