© 1995 by Oxford University Press
Original Articles |
Generalized Quantifiers and Logical Reducibilities
Department of Computer Science, University College of Swansea Swansea SA2 8PP, UK. E-mail: a.dawar{at}swansea.ac.uk
We consider the problem of defining a logic that captures exactly the polynomial time computable properties of finite structures, by extending first-order logic (FO) and fixed-point logic (FP) by means of Lindstrom quantifiers. In particular,we define infinite uniform sequences of quantifiers and show that these correspond to a natural notion of logical reducibility. We show that if there is any logic that captures the complexity class PTTME, in the sense of a recursive enumeration of PTIME properties, then there is one that is an extension of FO by a uniform sequence of quantifiers. This is established through a general result linking the existence of complete problems for a complexity class to the existence of recursive index sets for the class, for a wide variety of complexity classes.
Keywords: Finite model theory; polynomial time computability; complexity theory; logical reducibilities.