In this work there is established an optimal existence and regularity theory
for second order linear parabolic differential equations on a large class of
noncompact Riemannian manifolds. Then it is shown that it provides a general
unifying approach to problems with strong degeneracies in the interior or at
the boundary.Comment: To appear in "Recent Developments of Mathematical Fluid Mechanics",
Series: Advances in Mathematical Fluid Mechanics, Birkhaeuser-Verlag,
Editors: G. P. Galdi, J. G. Heywood and R. Rannacher. Some misprints of the
earlier version have been correcte