1. V. N. Vragov, “On the theory of boundary-value problems for equations ofmixed type in space,” Differ. Uravn. 13 (6), 1098–1105 (1977).
2. V. N. Vragov, “On the statement and solvability of boundary-value problems for equations of mixedcompound type,” in Mathematical Analysis and Related Problems of Mathematics (Nauka, Novosibirsk, 1978), pp. 5–13 [in Russian].
3. I. E. Egorov and V. E. Fedorov, Nonclassical Higher-Order Equations in Mathematical physics (Computer Center, Russian Academy of Sciences, Sibirsk. Branch, Novosibirsk, 1995) [in Russian].
4. A. N. Terekhov, “the boundary-value problem of equations ofmixed type. Functional analysismethods used to solve problems ofmathematical physics and computationalmathematics,” in Collection of Scientific Papers (Inst.Math., Russian Academy of Sciences, Sibirsk. Branch, Novosibirsk, 1979), pp. 128–137 [in Russian].
5. I. E. Egorov and T. I. Zakharova, “On the Fredholm property of the boundary-value problem for equations of mixed type,” Mat. Zametki, Yakutsk State Univ. 20 (1), 20–26 (2013).