An Isomorphism Criterion for Completely Decomposable Abelian Groups. J. de Groot de Mathematische Annalen
The compactness operator in general topology de Groot, J. — 1967 General Topology and its Relations to Modern Analysis and Algebra
Linearization of mappings de Groot, J. — 1962 General Topology and its Relations to Modern Analysis and Algebra
On the topological characterization of manifolds de Groot, J. — 1972 General Topology and its Relations to Modern Analysis and Algebra
Inductive compactness as a generalization of semicompactness J. de Groot; T. Nishiura — 1966 Fundamenta Mathematicae
Compactness as an operator J. de Groot; H. Herrlich; G. E. Strecker; E. Wattel — 1969 Compositio Mathematica