Interpretation methods and their restrictions to polynomials have been deeply used to control the termination and complexity of first-order term rewrite systems. This paper extends interpretation methods to a pure higher order functional language. We develop a theory of higher order functions that is well-suited for the complexity analysis of this programming language. The interpretation domain is a complete lattice and, consequently, we express program interpretation in terms of a least fixpoint. As an application, by bounding interpretations by higher order polynomials, we characterize Basic Feasible Functions at any order.
The present paper is an extended version of the results in @cite_0 : more proofs and examples have been provided. An erratum has been provided: the interpretation of the case construct has been slightly modified so that we can consider non decreasing functions (and not only strictly increasing functions). There are two lines of work that are related to our approach. @cite_15 , Van De Pol introduced higher order interpretation for showing the termination of higher order term rewrite systems. @cite_18 @cite_20 , Baillot and Dal Lago introduce a higher order interpretations for complexity analysis of term rewrite systems. While the first work only deals with termination properties, the second work is restricted to a family of higher order term rewrite systems called simply typed term rewrite systems.
@cite_0 @cite_15 @cite_18 @cite_20
1505645573 2964098951 1568506451 2075296484
This paper explores how to extend the dependency pair technique for proving termination of higher-order rewrite systems. We show that the termination property of higher-order rewrite systems can be checked by the non-existence of an infinite R-chain, which is an extension of Arts’ and Giesl’s result for the first-order case. It is clarified that the subterm property of the quasi-ordering, used for proving termination automatically, is indispensable. Arts and Giesl proved that the termination of a first-order rewrite system can be reduced to the study of its dependency pairs''. We extend these results to rewrite systems on simply typed lambda-terms by using Tait's computability technique. This paper expands the termination proof techniques based on the lexicographic path ordering to term rewriting systems over varyadic terms, in which each function symbol may have more than one arity. By removing the deletion property from the usual notion of the embedding relation, we adapt Kruskal’s tree theorem to the lexicographic comparison over varyadic terms. The result presented is that finite term rewriting systems over varyadic terms are terminating whenever they are compatible with the lexicographic path order. The ordering is simple, but powerful enough to handle most of higher-order rewriting systems without λ-abstraction, expressed as S-expression rewriting systems. A natural term rewriting framework for the Bellantoni Cook schemata of predicative recursion, which yields a canonical definition of the polynomial time computable functions, is introduced. In terms of an exponential function both, an upper bound and a lower bound are proved for the resulting derivation lengths of the functions in question. It is proved that any natural reduction strategy yields an algorithm which runs in exponential time. We give an example in which this estimate is tight. It is proved that the resulting derivation lengths become polynomially bounded in the lengths of the inputs if the rewrite rules are only applied to terms in which the safe arguments – no restrictions are assumed for the normal arguments – consist of values, i.e. numerals, and not of names, i.e. non numeral terms. It is proved that in the latter situation any inside first reduction strategy and any head reduction strategy yield algorithms, for the function under consideration, for which the running time is bounded by an appropriate polynomial in the lengths of the input. A feasible rewrite system for predicative recursion with predicative parameter substitution is defined. It is proved that the derivation lengths of this rewrite system are polynomially bounded in the lengths of the inputs. As a corollary we reobtain Bellantoni’s result stating that predicative recursion is closed under predicative parameter recursion.