Monadic second-order logic on tree-like structures
An operation M* which constructs from a given structure M a tree-like structure whose domain consists of the finite sequences of elements of M is considered. A notion of automata running on such tree-like structures is defined. It is shown that automata of this kind characterise expressive power of monadic second-order logic (MSOL) over tree-like structures. Using this characterisation it is proved that MSOL theory of a tree-like structure is effectively reducible to that of the original structure. As another application of the characterisation it is shown that MSOL on trees of arbitrary degree is equivalent to first-order logic extended with unary least fixpoint operator. (C) 2002 Elsevier Science B.V. All rights reserved.
monadic second-order logic tree automata decidability