1. S. L. Sobolev, ‘‘On a new problem of mathematical physics,’’ Izv. Akad. Nauk SSSR, Ser. Mat. 18, 3–50 (1954).
2. G. I. Barenblatt, Yu. P. Zheltov, and I. N. Konina, ‘‘On the basic concepts of filtration theory in fractured media,’’ Prikl. Mat. Mekh. 24 (5), 58–73 (1960).
3. T. W. Ting, ‘‘Parabolic and pseudoparabolic partial differential equations,’’ J. Math. Soc. Jpn. 14, 1–26 (1969).
4. T. B. Benjamin, J. L. Bona, and J. J. Mahony, ‘‘Model equations for long waves in nonlinear dispersive systems,’’ Phil. Trans. R. Soc. London, Ser. A 272 (1220), 47–78 (1972).
5. R. E. Showalter and T. W. Ting, ‘‘Pseudoparabolic partial differential equations,’’ SIAM J. Math. Anal. 1, 1–26 (1970).