HOL4 vs Isabelle
| HOL4 | Isabelle | |
|---|---|---|
| Free plan | No | Yes |
| Free trial | No | No |
| Paid from | — | Free |
| Open source | No | No |
| Platforms | Windows, Linux | Linux, macOS, self-hosted, Windows |
| Free plan | Yes | Yes |
| Supported formalisms | theorem-proving | theorem-proving |
| Counterexamples | Yes | Yes |
| Proof artifacts | Yes | Yes |
| Input languages | HOL higher-order logic; Standard ML | Isabelle/Isar, Isabelle/Pure, ML; executable specifications can generate SML, OCaml, Haskell, and Scala |
| Deployment | self-hosted | self-hosted |
| Verification method | — | deductive |
Both are listed in Best Formal Verification Tools. On Freedom251, Isabelle scores higher on our published basis.