We study the propagation of the analytic regularity of the C∞ solutions of the quasi-linear, weakly hyperbolic wave equation u tt - a(u)u xx = 0, where a(u) is a bounded, nonnegative analytic function.
"Propagation of analyticity in the C∞ solutions of quasi-linear weakly hyperbolic wave equations." Tsukuba J. Math. 35 (1) 13 - 52, June 2011. https://doi.org/10.21099/tkbjm/1311081447