Gamkrelidze, R. V. Journal of Dynamical and Control Systems, 5, 4, 1999, pàg. 437–451. DOI: 10.1023/A:1021783020548. Reprinted in Bolibruch. Mathematical Events of the Twentieth Century. Berlin: Springer, 2006, p. 85–99. ISBN 3-540-23235-4.
For first published works, see references in Fuller, A. T. J. Electronics & Control, 15, 5, 1963, pàg. 513–517. DOI: 10.1080/00207216308937602.