Barreledness of subspaces of countable codimension and the closed graph theorem D. Van Dulst — 1972 Compositio Mathematica
Total Bounded Extensions of Biorthogonal Sequences in Banach Spaces. D. van Dulst — 1974 Mathematische Annalen
Perturbation theory and strictly singular operators in locally convex spaces D. van Dulst — 1970 Studia Mathematica