Source: Rocky Mountain J. Math.
Volume 36, Number 4
R. Courant and D. Hilbert, Methods of mathematical physics, Vol. I, Interscience, New York, 1966.
Mathematical Reviews (MathSciNet): MR65391
Ju.I. Domšlovk, On the oscillation of solutions of vector differential equations, Soviet Math. Dokl. 11 (1970), 839-841.
Y.K. Li, Oscillation of systems of hyperbolic differential equations with deviating arguments, Acta Math. Sinica 40 (1997), 100-105 (in Chinese).
W.N. Li, Oscillation properties for systems of hyperbolic differential equations of neutral type, J. Math. Anal. Appl. 248 (2000), 369-384.
W.N. Li and B.T. Cui, Oscillation for systems of parabolic equations of neutral type, Southeast Asian Bull. Math. 23 (1999), 447-456.
--------, Oscillation for systems of neutral delay hyperbolic differential equations, Indian J. Pure Appl. Math. 31 (2000), 933-948.
W.N. Li and L. Debnath, Oscillation of a system of delay hyperbolic differential equations, Int. J. Appl. Math. 2 (2000), 417-431.
W.N. Li and F.W. Meng, Oscillation for systems of neutral partial differential equations with continuous distributed deviating arguments, Demonstratio Math. 34 (2001), 619-633.
E. Minchev and N. Yoshida, Oscillation of solutions of vector differential equations of parabolic type with functional arguments, J. Comput. Appl. Math. 151 (2003), 107-117.
E.S. Noussair and C.A. Swanson, Oscillation theorems for vector differential equations, Util. Math. 1 (1972), 97-109.
Mathematical Reviews (MathSciNet): MR306685
--------, Oscillation of nonlinear vector differential equations, Ann. Mat. Pura Appl. 109 (1976), 305-315.
Mathematical Reviews (MathSciNet): MR425321
J. Wu, Theory and applications of partial functional differential equations, Springer-Verlag, New York, 1996.