The problem of exact observability is analyzed for a wide class of neutral
type systems by an infinite dimensional approach. The duality with the exact
controllabil-ity problem is the main tool. It is based on an explicit
expression of a neutral type system which corresponding to the abstract adjoint
system. A nontrivial relation is obtained between the initial neutral system
and the system obtained via the adjoint abstract state operator. The
characterization of the duality between controllability and observability is
deduced, and then observability conditions are obtained.Comment: Accepted in Systems and Control Letter
