Hirosawa, Fumihiko, and Michael Reissig. “About the Optimality of Oscillations in Non-Lipschitz Coefficients for Strictly Hyperbolic Equations”. ANNALI SCUOLA NORMALE SUPERIORE - CLASSE DI SCIENZE 3, no. 3 (December 14, 2009): 589-608. Accessed May 28, 2025. http://20.103.181.36/index.php/annaliscienze/article/view/49.