Abstract We describe practical experiments of program verification in the frame of the Theorema system. This includes both imperative programs (using Hoare logic), as well as functional programs (using fixpoint theory). For a certain class of imperative programs we are able to generate automatically the loop invariants and then verification conditions, by using combinatorial and algebraic techniques. Verification conditions for functional recursive programs are derived and soundness theorem is proven. The verification conditions in both cases are generated as natural-style predicate logic formulae, which can be then proven by Theorema, by issuing naturalstyle proofs which are human–readable.

We study and implement concrete methods for the verification of both imperative as well as functional programs in the frame of the Theorema system. The distinctive features of our approach consist in the automatic generation of loop invariants (by using combinatorial and algebraic techniques), and the generation of verification conditions as first–order logical formulae which do not refer to a specific model of computation.

We describe a sound, terminating, and complete matching algorithm for terms built over flexible arity function symbols and context, function, sequence, and individual variables. Context and sequence variables allow matching to move in term trees to arbitrary depth and breadth, respectively. The values of variables can be constrained by regular expressions which are not necessarily linear. We describe heuristics for optimization, and discuss applications.

Abstract. We present a method for generating polynomial invariants for a subfamily of imperative loops operating on numbers, called the P-solvable loops. The method uses algorithmic combinatorics and algebraic techniques. The approach is shown to be complete for some special cases. By completeness we mean that it generates a set of polynomial invariants from which, under additional assumptions, any polynomial invariant can be derived. These techniques are implemented in a new software package Aligator written in Mathematica and successfully tried on many programs implementing interesting algorithms working on numbers. 1

Abstract — We present a verification environment for imperative programs (using Hoare logic) and for functional programs (using fixpoint theory) in the frame of the Theorema system (www.theorema.org). In particular, we discuss some methods for finding the invariants of loops and specifications of auxiliary tail recursive functions. These methods use techniques from (polynomial) algebra and combinatorics, namely Groebner bases, variable elimination and symbolic summation (the Gosper algorithm, the technique of generating functions). The methods are demonstrated on several examples which have been treated automatically by our implementation. Index Terms — program analysis and verification, loop invariant generation, theorem proving, symbolic summation I.

We have developed a program for inductive theory formation, called IsaCoSy, which synthesises conjectures ‘bottom-up’ from the available constants and free variables. The synthesis process is made tractable by only generating irreducible terms, which are then filtered through counter-example checking and passed to the automatic inductive prover IsaPlanner. The main technical contribution is the presentation of a constraint mechanism for synthesis. As theorems are discovered, this generates additional constraints on the synthesis process. We evaluate IsaCoSy as a tool for automatically generating the background theories one would expect in a mature proof assistant, such as the Isabelle system. The results show that IsaCoSy produces most, and sometimes all, of the theorems in the Isabelle libraries. The number of additional un-interesting theorems are small enough to be easily pruned by hand.

We study matching in flat theories both from theoretical and practical points of view. A flat theory is defined by the axiom f(x, f(y), z). = f(x, y, z) that indicates that nested occurrences of the function symbol f can be flattened out. From the theoretical side, we design a procedure to solve a system of flat matching equations and prove its soundness, completeness, and minimality. The minimal complete set of matchers for such a system can be infinite. The procedure enumerates this set and stops if it is finite. We identify a class of problems on which the procedure stops. From the practical point of view, we look into restrictions of the procedure that give an incomplete terminating algorithm. From this perspective, we give a set of rules that, in our opinion, describes the precise semantics for the flat matching algorithm implemented in the Mathematica system. 1.

Abstract—As an extension of our previous work on imperative program verification, we present a formalism for handling the total correctness of While loops in imperative programs, consisting in functional based definitions of the verification conditions for both partial correctness and for termination. A specific feature of our approach is the generation of verification conditions as first order formulae, including the termination condition which is expressed as an induction principle. Keywords-program analysis and verification, symbolic execution, theorem proving I.

Sequence variables play an interesting role in unification and matching when dealing with terms in an unranked signature. Sequence Unification generalizes Word Unification and seems to be appealing for information extraction in XML documents, program transformation, and rule-based programming. In this work we study a relation between Sequence Unification and another generalization of Word Unification: Context Unification. We introduce a variant of Context Unification, called Left-Hole Context Unification that

Abstract. An axiomatic theory represents mathematical knowledge declaratively as a set of axioms. An algorithmic theory represents mathematical knowledge procedurally as a set of algorithms. A biform theory is simultaneously an axiomatic theory and an algorithmic theory. It represents mathematical knowledge both declaratively and procedurally. Since the algorithms of algorithmic theories manipulate the syntax of expressions, biform theories—as well as algorithmic theories—are difficult to formalize in a traditional logic without the means to reason about syntax. Chiron is a derivative of von-Neumann-Bernays-Gödel (nbg) set theory that is intended to be a practical, general-purpose logic for mechanizing mathematics. It includes elements of type theory, a scheme for handling undefinedness, and a facility for reasoning about the syntax of expressions. It is an exceptionally well-suited logic for formalizing biform theories. This paper defines the notion of a biform theory, gives an overview of Chiron, and illustrates how biform theories can be formalized in Chiron. 1