Proposition 30.5.4.label Let $\ell^{1}(\integer)$ be the convolution algebra on $\integer$ and $f \in \ell^{1}(\integer)$, then
\[\sigma(f) = \bracs{\sum_{n \in \integer}f(n)z^n \bigg | z \in \partial B_\complex(0, 1)}\]
Proof. By Theorem 30.5.3 and (4) of Proposition 29.8.2.$\square$
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