cvc5 vs Isabelle

cvc5 is a free, open-source solver for satisfiability modulo theories problems. It determines whether first-order formulas are satisfiable or valid across combinations of background theories, including arrays, bit-vectors, floating-point numbers, arithmetic, and strings. It also has a Syntax-Guided Synthesis engine for synthesizing functions against those theories.

The solver can run as a standalone command-line tool or be used as a library, with C++, C, Java, and Python APIs. Its binary accepts SMT-LIB v2 and SyGuS-IF input, and it can produce proofs and unsatisfiable cores to explain unsatisfiability results. The project links to an online interface for running SMT-LIB scripts and provides source releases and binaries for Linux, macOS, and Windows. cvc5 is led jointly by Stanford University and the University of Iowa. Research and commercial use are described as essentially unrestricted. The default license is modified BSD; using optional GPLv3 dependencies makes the combined work subject to GPLv3.

Isabelle is a free proof assistant for expressing mathematical formulas in a formal language and proving them within a logical calculus. Its main applications are formalizing mathematics and verifying properties of hardware, software, programming languages, and protocols. Isabelle/HOL provides a higher-order logic environment for large applications, with tools for reasoning, simplification, linear arithmetic, algebraic decision procedures, and access to external first-order provers through Sledgehammer. Proofs can be written in Isar, a structured language intended to be understandable to people and computers. Isabelle/HOL can generate SML, OCaml, Haskell, and Scala code from executable specifications. Isabelle/jEdit is the default interface, providing ongoing proof checking and real-time feedback; the Isabelle2025-2 release also includes Isabelle/VSCode with panels for documentation, symbols, and Sledgehammer. The distribution includes a library of verified mathematics, supplemented by the Archive of Formal Proofs. Isabelle runs on Linux, macOS, Windows, and self-hosted deployments. Its main code base is subject to BSD-style regulations. Windows lacks developer signatures and certificates and is rejected by Microsoft by default at first launch; macOS requires users to allow the unsigned application to open.