  The Kondo insulator (KI) is studyed in the frameworrk of one dimensional
models of Kondo and symmentic Anderson lattices at half filling. The consistent
application of the mean field approach and the solution using the Bethe ansatz
made it possible to come close to solving the problem of the ground state of
KI. It is shown, that in ${Z}_2$-field electrons and local moments form
singlets at each lattice site. This field leads to an on-site interaction, on
which electrons are scattered. In the Kondo chain the Kondo insulator is
similar to the Mott insulator in the Hubbard chain. The advantage of proposed
approach is that it is possible to solve the problem for arbitrary exchange
interaction constant. In the Anderson lattice, the indirect on-site interaction
between band electrons is attractive, which makes it possible to propose a new
mechanism for high $T_c$ superconductivity in real compounds.
