On the Barenblatt Equation of Elastoplastic Filtration S. KaminL. PeletierJuan Vazquez Indiana University Mathematics Journal 1991 text pdf 10.1512/iumj.1991.40.40060 10.1512/iumj.1991.40.40060 en Indiana Univ. Math. J. 40 (1991) 1333 - 1362 state-of-the-art mathematics http://iumj.org/access/