Quantum finite automata with mixed states are proved to be super-exponentially more concise rather than quantum finite automata with pure states. It was proved earlier by A. Ambainis and R. Freivalds that quantum finite automata with pure states can have an exponentially smaller number of states than deterministic finite automata recognizing the same language. There was an unpublished ‘‘folk th...

Using a result of B.H. Neumann we extend Eilenberg’s Equality Theorem to a general result which implies that the multiplicity equivalence problem of two (nondeterministic) multitape finite automata is decidable. As a corollary we solve a long standing open problem in automata theory, namely, the equivalence problem for multitape deterministic finite automata. The main theorem states that there ...

There is a well known relationship between alternating automata on finite words and symbolically represented nondeterministic automata on finite words. This relationship is of practical relevance because it allows to combine the advantages of alternating and symbolically represented nondeterministic automata on finite words. However, for infinite words the situation is unclear. Therefore, this ...

In this paper we study the problem of minimising deterministic automata over finite and infinite words. Deterministic finite automata are the simplest devices to recognise regular languages, and deterministic Büchi, Co-Büchi, and parity automata play a similar role in the recognition of ω-regular languages. While it is well known that the minimisation of deterministic finite and weak automata i...

Inoue et al. introduced an automaton on a twodimensional tape, which decides acceptance or rejection of an input tape by scanning the tape from various sides by various automata which move one way, and investigated the accepting power of such an automaton. This paper continues the investigation of this type of automata, especially, ∨-type automata (obtained by combining four three-way two-dimen...

Semi-input-memory finite automata are a generalization of input-memory finite automata by appending an autonomous finite automaton component. This paper gives a decision criterion of weakly invertible semi-input-memory finite automata with delay 2 of which the minimal output weight of length 2 and the sizes of input and output alphabets are identical. The results are used to generate a kind of ...