  In this paper, I introduce two new concepts (Minkowski quasi-photon and
invariance of physical definitions) to elucidate the theory developed in my
previous work [Can. J. Phys. 93, 1510 (2015)], and to clarify the criticisms by
Partanen and coworkers [Phys. Rev. A 95, 063850 (2017)]. Minkowski quasi-photon
is the carrier of the momentum and energy of light in a medium under the sense
of macroscopic averages of light-matter microscopic interactions. I firmly
argue that required by the principle of relativity, the definitions of all
physical quantities are invariant. I shed a new light on the significance of
the symmetry of physical laws for resolution of the Abraham-Minkowski debate on
the momentum of light in a medium. I illustrate by relativistic analysis why
the momentums and energies of the electromagnetic subsystem and the material
subsystem form Lorentz four-vectors separately for a closed system of
light-matter interactions, and why the momentum and energy of a non-radiation
field are owned by the material subsystem, and they are not measurable
experimentally. Finally, I also provide an elegant proof for the invariance of
physical definitions, and a clear definition of the Lorentz covariance for
general physical quantities and tensors.
