He has supervised a number of graduate theses and projects. He was an advisor of 16 doctoral candidates both in mathematics and computer science. In particular, he advised dissertations in mathematics by Małgorzata Dubiel-Lachlan, Roman Kossak, Adam Krawczyk, Tadeusz Kreid, Roman Murawski, Andrzej Pelc, Zygmunt Ratajczyk, Marian Srebrny, and Zygmunt Vetulani. In computer science his students were V. K. Cody Bumgardner, Waldemar W. Koczkodaj, Witold Lipski, Joseph Oldham, Inna Pivkina, Michael Vladyslav Sobolewski, Paweł Traczyk, and Zygmunt Vetulani. All these individuals has worked in the various institutions of higher education in Canada, France, Poland, and the United States.
Mathematics
He investigated a number of areas in the foundations of mathematics, for instance infinitary combinatorics, metamathematics of set theory, the hierarchy of constructible sets, models of second-order arithmetic, the impredicative theory of Kelley–Morse classes. He proved that the so-called Fraïssé conjecture is entailed by Gödel's axiom of constructibility. Together with Marian Srebrny, he investigated properties of gaps in a constructible universe.
Computer science
He studied logical foundations of computer science. In the early 1970s, in collaboration with Zdzislaw Pawlak, he investigated Pawlak's information storage and retrieval systems which then was a widely studied concept, especially in the Eastern Europe. These systems were, essentially a single-table relational databases, but unlike Codd's relational databases were bags rather than sets of records. These investigations, in turn, led Pawlak to the concept of rough set, studied by Marek and Pawlak in 1981. The concept of rough set, in computer science, statistics, topology, universal algebra, combinatorics, and modal logic, turned out to be an expressive language for describing, and especially manipulating an incomplete information.
Logic
In the area of nonmonotonic logics, a group of logics related to artificial intelligence, he focused on investigations of Reiter's Deault Logic, and autoepistemic logic of R. Moore. These investigations led to a form of Logic Programming called Answer Set Programming a computational knowledge representation formalism, studied both in Europe and in the United States. Together with Mirosław Truszczynski, he proved that the problem of existence of stable models of logic programs is NP-complete. In a stronger formalism admitting function symbols, along with Nerode and Remmel he showed that the analogous problem is Σ-complete.
Publications
V. W. Marek is an author of over 180 scientific papers in the area of foundations of mathematics and of computer science. He was also an editor of numerous proceedings of scientific meetings. Additionally, he authored or coauthored several books. These include: