14. Among his PhD students were Ton Anbeek (doct. in 1978; full professor at Leiden University in 1982); Gilles Dorleijn (doct. in 1984; full professor at University of Groningen in 1985); Wiljan van den Akker (doct. in 1986; full professor at Utrecht University in 1988); Wiel Kusters (doct. 1986; full professor at Maastricht University in 1989); and Marita Mathijsen (doct. in 1987; full professor at the University of Amsterdam in 1999). Notwithstanding the qualities of the individual professors, given the basic criteria for a healthy scientific community this situation is of course highly remarkable.