Complex strongly hyperbolic 4×4 systems, reduced dimension and hermitian systems

In the case of real coefficients, the results were extended to the case of variable coefficients [T. Nishitani, J. Vaillant, Tsukuba J. Math. 25 (2001) 165; ibid. 27 (2003) 389]; the authors prepare the extension theorem to the case of complex variable coefficients.