  Recently Russell et al. [Phys. Rev. Lett. 120, 047401 (2018)] have reported a
clear signal of many-particle contributions to cyclotron resonance in
high-mobility hBN-encapsulated graphene, observing significant variations of
resonance energies as a function of the filling factor $\nu$ for a series of
interband channels. To elucidate their results, Coulombic contributions to the
Landau-level spectra and cyclotron resonance in graphene are examined with a
possible band gap taken into account and with emphasis on revealing
electron-hole ($eh$) conjugation symmetry underlying such level and resonance
spectra. Theory, based on the single-mode approximation, gives a practically
good account of the experimental data; the data suggest a band gap of ~ 10 meV
and show a profile that apparently reflects $eh$ conjugation symmetry.
