At the turning of the millennium, a switch in computing technology is forecasted and looked
for. Two main directions of research, both based on quite unconventional ideas are most …

After recalling the definition of decidability and universality, we first give a survey of results
on the as exact as possible border betweeen a decidable problem and the corresponding …

We survey some work concerned with small universal Turing machines, cellular automata,
tag systems, and other simple models of computation. For example, it has been an open …

A reversible Turing machines is a computing model with a “backward deterministic” property,
which is closely related to physical reversibility. In this paper, we study the problem of finding …

Factorizing composite number n= qr, where q and r are two large primes, and finding
discrete logarithm modulo large prime number p are two difficult computational problems …

We survey some work concerned with small universal Turing machines, cellular automata,
tag systems, and other simple models of computation. For example it has been an open …

We are interested by “small” Universal Turing Machines (in short: UTMs), in the framework of
2, 3 or 4 tape—symbols. In particular: tape—symbols. Apart from the old 24—states machine …

Computational completeness is known for P systems with two catalysts and purely catalytic
P systems with three catalysts as well as for P systems with one bi-stable catalyst. We …

A Universal Turing Machine with 3 States and 9 Symbols Page 1 A Universal Turing Machine with
3 States and 9 Symbols Manfred Kudlek 1 and Yurii Rogozhin 2 1 Fachbereich Informatik …

Numerous results for simple computationally universal systems are presented, with a
particular focus on small universal Turing machines. These results are towards finding the …