@article{CM_1969__21_4_349_0,
     author = {de Groot, J. and Herrlich, H. and Strecker, G. E. and Wattel, E.},
     title = {Compactness as an operator},
     journal = {Compositio Mathematica},
     pages = {349--375},
     publisher = {Wolters-Noordhoff Publishing},
     volume = {21},
     number = {4},
     year = {1969},
     mrnumber = {259861},
     zbl = {0186.55902},
     language = {en},
     url = {http://www.numdam.org/item/CM_1969__21_4_349_0/}
}