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Published online by Cambridge University Press: 15 February 2013
Towards an involutive analogue of a result on the semisimplicity of ${\ell }^{1} (S)$ by Hewitt and Zuckerman, we show that, given an abelian
$\ast $-semigroup
$S$, the commutative convolution Banach
$\ast $-algebra
${\ell }^{1} (S)$ is
$\ast $-semisimple if and only if Hermitian bounded semicharacters on
$S$ separate the points of
$S$; and we search for an intrinsic separation property on
$S$ equivalent to
$\ast $-semisimplicity. Very many natural involutive analogues of Hewitt and Zuckerman’s separation property are shown not to work, thereby exhibiting intricacies involved in analysis on
$S$.