Team, S. “Linear Time-Varying Systems in Hilbert Spaces: Exact Controllability Implies Complete Stabilizability: P. Niamsup, V. N. Phat”. Thai Journal of Mathematics, vol. 7, no. 1, June 2009, pp. 189-9, https://thaijmath2.in.cmu.ac.th/index.php/thaijmath/article/view/154.