Abstract A string diagram is a two-dimensional graphical representation that can be described as a one-dimensional term generated from a set of primitives using sequential and parallel compositions. Since different syntactic terms may represent the same diagram, this syntax is quotiented by a collection of coherence equations expressing equivalence up to deformation. This work lays foundations for automated reasoning about diagrammatic equivalence, motivated primarily by the verification of quantum circuit equivalences. We consider two classes of diagrams, for which we introduce normalizing term rewriting systems that equate diagrammatically equivalent terms. In both cases, we prove termination and confluence with the help of the proof assistant Isabelle/HOL.

The free-variable tableau method has been widely used in order to automate proofs in multiple kinds of logics. Many automated theorem provers rely on this approach, either because it is the only available method - e.g. in certain modal logics - or because it facilitates the generation of proof certificates. However, as far as the authors know, its results have never been formalized in a proof assistant. In this paper, we present TableauxRocq, a deep embedding of free-variable first-order tableaux in the Rocq prover. The formalized calculus is proved sound and provides a modular Skolemization system that enables the use of Skolemization-based optimizations. Moreover, we show how TableauxRocq can be used as a certifier for automated theorem provers by adapting the Goeland prover - that can already output Rocq terms - to output proofs in the TableauxRocq format. By using the power of reflection, thereby providing a fully certified proof checker for free, we show that Goeland’s exported Rocq terms and TableauxRocq’s proof certificates can be checked in a similar time frame without proof optimizations, and that the latter has strictly better performances in presence of Skolemization-related optimizations.

Abstract We introduce SC-TPTP, an extension of the TPTP derivation format that supports sequent formalism, enabling seamless proof exchange between interactive theorem provers and first-order automated theorem provers. We provide a way to represent non-deductive steps—Skolemization, clausification, and Tseitin normal form—as deductive steps within the format. Building upon the existing support in the Lisa proof assistant and the Goéland theorem prover, SC-TPTP ecosystem is further enhanced with proof output interfaces for Egg and Prover9, as well as proof reconstruction support for HOL Light, Lean, and Rocq.

In this paper, we present a general strategy that enables the translation of tableau proofs using different Skolemization rules into machine-checkable proofs. It is part of a framework that enables (i) instantiation of the strategy into algorithms for different sets of tableau rules (e.g., different logics) and (ii) easy soundness proof which relies on the local extensibility of user-defined rules. Furthermore, we propose an instantiation of this strategy for first-order tableaux that handles notably pre-inner Skolemization rules, which is, as far as the authors know, the first one in the literature. This deskolemization strategy has been implemented in the Goéland [17] automated theorem prover, enabling an export of its proofs to Coq [8] and Lambdapi [2]. Finally, we have evaluated the algorithm performances for inner and pre-inner Skolemization rules through the certification of proofs from some categories of the TPTP [39] library.