@article {1305.1133,
	title = {A note on non-homogeneous hyperbolic operators with low-regularity coefficients},
	year = {2013},
	abstract = {<p>In this paper we obtain an energy estimate for a complete strictly hyperbolic operator with second order coefficients satisfying a log-Zygmund-continuity condition with respect to $t$, uniformly with respect to $x$, and a log-Lipschitz-continuity condition with respect to $x$, uniformly with respect to $t$.</p>},
	author = {Ferruccio Colombini and Francesco Fanelli}
}
