1. V. A. Sadovnichii, Operator Theory (Izd. Mosk. Univ., Moscow, 1971) [in Russian].
2. O. G. Smolyanov, in Trends in Stochastic Analysis (Cambridge Univ. Press, Cambridge, 2009), pp. 283–302.
3. V. A. Sadovnichii, O. G. Smolyanov, and E. T. Shavgulidze, Dokl. Math. 86, 644–647 (2012).
4. O. G. Smolyanov and E. T. Shavgulidze, Continual Integrals (Izd. Mosk. Univ., Moscow, 1990) [in Russian].
5. K. J. Engel, One-Parameter Semigroups for Linear Evolution Equations (Springer-Verlag, Berlin, 2000).