An Inefficient Representation of the Empty Word

From July 1978 till the summer of 1980 Paul Vitányi and I shared an office at Mathematical Centre (former name of C.W.I.), located at Tweede Boerhaavestraat 49 in the Oosterpark-neighborhood of Amsterdam. A couple of weeks after I arrived, Paul and I moved together with Arie de Bruin to a freshly painted room which happened to be the half of a former class room, like many offices in that old school building, separated from its companion by a rather thin wall. Without difficulty or any intention we could hear at least 50% of our neighbors’ conversations as they could from ours. And the view from our room was something special too: a 19th century part of the former Amstel brewery which happened to be of too little interest to industrial archeology in order to survive in later days. Another well-known feature of the old Mathematical Centre was its library: famous for its outstanding collection of books, journals and reports on mathematics and computer science, and remarkable for the dishes of rat poison on the floors, inviting the nightly intruders to commit suicide rather than nibbling at the precious volumes. In 1978 both Paul and I finished our Ph.D. work on parallel rewriting, although our theses have very little in common; cf. [1, 7]. But we both had the intention to change our subject into the direction of computational complexity: a subject in which Paul achieved much more than I did; see e.g. [4], which also gives me the opportunity to turn to a more serious matter that is related to the title of this note.