Nudel’manA. A. “Extension of the Stieltjes Moment Sequence to the Left and Related Problems of the Spectral Theory of Inhomogeneous String”. Ukrains’kyi Matematychnyi Zhurnal, Vol. 59, no. 6, June 2007, pp. 815–825, https://umj.imath.kiev.ua/index.php/umj/article/view/3347.