In this treatise we present the semigroup approach to quasilinear
evolution equa- of parabolic type that has been developed over the last
ten years, approxi- tions mately. It emphasizes the dynamic viewpoint
and is sufficiently general and flexible to encompass a great variety of
concrete systems of partial differential equations occurring in science,
some of those being of rather 'nonstandard' type. In partic- ular, to
date it is the only general method that applies to noncoercive systems.
Although we are interested in nonlinear problems, our method is based on
the theory of linear holomorphic semigroups. This distinguishes it from
the theory of nonlinear contraction semigroups whose basis is a
nonlinear version of the Hille- Yosida theorem: the Crandall-Liggett
theorem. The latter theory is well-known and well-documented in the
literature. Even though it is a powerful technique having found many
applications, it is limited in its scope by the fact that, in concrete
applications, it is closely tied to the maximum principle. Thus the
theory of nonlinear contraction semigroups does not apply to systems, in
general, since they do not allow for a maximum principle. For these
reasons we do not include that theory.