  The Kondo insulator state (KIS) realized in the symmetric Anderson model at
half filling is studied in the framework of a mean field approach. It is shown
that the state of the Kondo insulator is realized in a lattice with a double
cell and a gapped electron liquid behaves like a gapless Majorana spin liquid.
The local moments of d-electrons form a static $Z_2$-field in which band
electrons move. The gap value in the quasi-particle excitations spectrum
decreases with increasing an external magnetic field and closes at its critical
value. The behavior of an electron liquid is studied for an arbitrary dimension
of the model. The proposed approach leads to the description of KIS without the
need to resort to artificial symmetry breaking to alternative understanding of
the physical nature of this phase state.
