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Published online by Cambridge University Press: 20 November 2018
Let U be a nonempty subset of a Banach space, S a left reversible semitopological semigroup,
a continuous representation of S as lipschitzian mappings on U into itself, that is for each s ∊ S, there exists ks > 0 such that
for x, y ∊ U. We first show that if there exists a closed subset C of U such that
then S with lim sups
has a common fixed point in a Hilbert space. Next, we prove that the theorem is valid in a Banach space E if lim sups 