  The higher-derivative theories with degenerate frequencies exhibit BRST
symmetry (O. Rivelles, Phys. Lett. B577 (2003), 147). In the present paper
meaning of BRST invariance condition is analyzed. The BRST symmetry is related
to nondiagonalizability of the Hamiltonian and it is shown that BRST condition
singles out the subspace spanned by proper eigenvectors of the Hamiltonian.
