The first author [Vestn. Mosk. Univ., Ser. XV 1983, No.3, 8-13 (1983; Zbl 0527.35008); English translation in Mosc. Univ. Comput. Math. Cybernetics 7 (1983)] considered the elliptic equation
and gave Kneser type estimates for its coefficients. In this paper new exact Kneser type estimates are provided. Such estimates were not known before, even in the case .