“…A. Dubinskii [9], A. A. Shkalikov [22], S. S. Mirzoev [18], A. R. Aliev [1]- [4], and for the operator-differential equations of the fourth order with multiple characteristics are studied, for example, in the paper by A. R. Aliev [5]. It should be noted that widely enough matters of solvability of operator-differential equations are studied in spaces without weight (see the books by S. G. Krein [16], J.-L. Lions, and E. Magenes [17], V. I. Gorbachuk, and M. L. Gorbachuk [14], J.…”