A ≡−d∕dx on BC0(R+),
𝒟(A) ≡{f ∈ BC0(R+)∣f′∈ BC0(R+)}, is an example of a maximal accretive
operator that does not generate a contraction semigroup. It does, however, have
extensions that generate uniformly bounded semigroups. A large class of
such extensions are presented. The same is done with d∕dx and −d∕dx on
C0[0,1].