1. Krein, S.G., Lineinye differentsial’nye uravneniya v banakhovom
prostranstve (Linear Differential Equations in a Banach Space), Moscow:
Nauka, 1967.
2. Goldstein, J.A., Semigroups of Linear Operators
and Applications, New York: Oxford Univ. Press, 1985. Translated under the title:
Polugruppy lineinykh operatorov i ikh prilozheniya,
Киев: Vyshcha Shk., 1989.
3. Vasil’ev, V.V., Krein, S.G., and Piskarev, S.I., Semigroups of operators, cosine
operator functions, and linear differential equations, J. Sov.
Math., 1991, vol. 54, no. 4, pp. 1042–1129.
4. Mel’nikova, I.V. and Filinkov, A.I., Integrated semigroups and
$$C
$$-semigroups. Well-posedness and regularization of
differential-operator problems, Russ. Math. Surv., 1994,
vol. 49, no. 6, pp. 115–155.
5. Glushak, A.V., Bessel operator function, Dokl.
Ross. Akad. Nauk, 1997, vol. 352, no. 5, pp. 587–589.