ON THE LOCAL SOLVABILITY FOR A NONLINEAR WEAKLY HYPERBOLIC EQUATION WITH ANALYTIC COEFFICIENTS
Communications in Partial Differential Equations Volume 26, Issue 5-6, 2001 Piero D'Anconaa* & Paola Trebeschib

pages 779-811
http://www.tandfonline.com/doi/abs/10.1081/PDE-100002378