Section: New Results
Pablo Arrighi and Gilles Dowek have studied the expression of mecanic motions in cellular automata. Part of this work has been published in TPNC  and another paper is in preparation.
Arnaud Spiwack developped a variant of Turing machine where the tape is replaced by an unlabeled tree. The additional structure makes combining machines much easier, making it tractable to give explicit descriptions of rather complex machines. The cost model of these machines models that of purely functional programming languages, making it possible to compare mathematically the complexity of imperative algorithms and of purely functional algorithms.