The Dirichlet problem for second order parabolic operators Kaj Nystrom caloric measuredoubling propertybackward in time Harnack inequalityarea integralmaximal functionsCarleson easureperturbation theory Indiana University Mathematics Journal 1997 text pdf 10.1512/iumj.1997.46.1277 10.1512/iumj.1997.46.1277 en Indiana Univ. Math. J. 46 (1997) 183 - 246 state-of-the-art mathematics http://iumj.org/access/