  The Blok-Esakia Theorem establishes that the lattice of superintuitionistic
logics is isomorphic to the lattice of extensions of Grzegorczyk's logic. We
prove that the Blok-Esakia isomorphism $\sigma$ does not extend to the
fragments of the corresponding predicate logics of already one fixed variable.
In other words, we prove that $\sigma$ is no longer an isomorphism from the
lattice of extensions of the monadic intuitionistic logic to the lattice of
extensions of the monadic Grzegorczyk logic.
