If X is a Banach space with the non-strict Opial property and r(X) (1) > 0
and C is a nonempty convex weakly compact subset of X, then every semigroup
T = {T-t : t is an element of G} of asymptotically regular selfmappings of
C with sigma (T) < 1 + r(X) (1) has a common fixed point.