1989 · Paul Veerkamp, Varol Akman, et al. · Centrum Wiskunde & Informatica (CWI), the national research institute for mathematics and computer science in the Netherlands · 10
1986 · P.J.W. teHagen, M.M. deRuiter · Centrum Wiskunde & Informatica (CWI), the national research institute for mathematics and computer science in the Netherlands · 1