Small Turing universal signal machines

Computation and universality have been defined in the 1930’s. In the last five or so decades, it has been unveiled how common they are. The question about the frontier moved from proving the universality of dynamical systems to the complexity of universal machines. This is not only an intellectual challenge, but also important to find niches escaping tons of non decidability results or otherwise assert that these niches are too small to be of any interest. There have already been a lot of investigations on small Turing machines (Rogozhin, 1982, 1996; Margenstern, 1995; Kudlek, 1996; Baiocchi, 2001), register machines (Korec, 1996), and cellular automata (Ollinger, 2002; Cook, 2004). Moreover, as (Turing) universality (capability to carry out any Turing/classical computation) has been developed in very limited systems, some “adaptations” were made and various notions of universality exist: