In this paper we show that from an estimate of the form $su{p}_{t\ge 0}\left|\right|C\left(t\right)-cos\left(at\right)I\left|\right|<1$, we can conclude that C(t) equals cos(at)I. Here ${\left(C\left(t\right)\right)}_{t\ge 0}$ is a strongly continuous cosine family on a Banach space.

We introduce the notion of a local n-times integrated C-semigroup, which unifies the classes of local C-semigroups, local integrated semigroups and local C-cosine functions. We then study its relations to the C-wellposedness of the (n + 1)-times integrated Cauchy problem and second order abstract Cauchy problem. Finally, a generation theorem for local n-times integrated C-semigroups is given.