1. BLOK, W. J., Varieties of interior algebras, PhD thesis, University of Amsterdam, 1976.
2. BLOK, W. J., ‘The lattice of modal logics (abstract)’, Bulletin of the Section of Logic of the Polish Academy of Sciences 6 (1977), 112–115.
3. BLOK, W. J., ‘On the degree of incompleteness of modal logics (abstract)’, Bulletin of the Section of Logic of the Polish Academy of Sciences 7 (1978), 167–175.
4. BLOK, W. J., ‘On the degree of incompleteness of modal logics and the covering relation in the lattice of modal logics’, Technical Report 78–07, Department of Mathematics, University of Amsterdam, 1978.
5. BLOK, W. J., ‘An axiomatization of the modal theory of the veiled recession frame’, Studia Logica 38 (1979) 37–47.