The development of the operator hierarchy has taken many years. Since my first realization of the central idea in 1992, I have profited greatly from discussions with and contributions by colleagues and friends (more or less in chronological order).

Nico van Straalen and Cees van Gestel (ecotoxicology and system science)
Claus Skovbo Jensen (Eigen and Schuster: the hypercycle)
Jørgen Axelsen, Christian Damgaard, Hans Løkke (ecotoxicology, system science and life)
Rolf Hoekstra
Didel Kornet
Peter Schippers
Francis Heylighen
Rob Hengeveld
Jeff Baldwin (correction of the Englisch of the first version of this site)
Henk Jan Bulten
Wiert Dijkkamp (this website reflects your creativity and passion for structured programming)

Last but not least I want to thank my wife and family for enduring my absentmindedness when I was struggling again with a 'tiny but relevant detail' of the 'last version' of the scheme