In modal logic with a necessity operator $\square$ and conditional connective $\to$, the axiom scheme $\text{Grz}$:

• • $\square \left(\square \left(\phi \to \square \phi \right)\to \phi \right)\to \phi$

Named after mathematician Andrzej Grzegorczyk (1922–2014), the least normal logic containing $\text{Grz}$ is notable for being a maximal modal companion to intuitionistic logic, that is, the largest modal logic into which intuitionistic logic may be embedded by means of the Gödel-McKinsey-Tarski translation.