**8. Conclusions**

Thus, the work obtained the necessary and sufficient conditions for approximate controllability for a class of degenerate fractional order evolution equations in terms of operators from the equation. The cases of infinite-dimensional and finite-dimensional input were studied. Using the concrete

control systems described by the initial-boundary value problems for the partial differential equations, the applications of the obtained abstract results were demonstrated.

**Author Contributions:** Conceptualization, D.B.; methodology, D.B. and V.E.F.; validation, D.M.G. and K.T.; formal analysis, V.E.F., D.M.G. and K.T.; investigation, D.M.G. and K.T.; Writing—Original Draft preparation, V.E.F.; Writing—Review and Editing, D.B. and V.E.F.; supervision, D.B. and V.E.F.; project administration, V.E.F. and D.M.G.

**Funding:** The reported study was funded by the Russian Foundation for Basic Research, project number 19-41-450001; by Act 211 of Government of the Russian Federation, contract 02.A03.21.0011; and by Ministry of Science and Higher Education of the Russian Federation, task number 1.6462.2017/BCh.

**Conflicts of Interest:** The authors declare no conflict of interest.
