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Let $T^r$ be the $r$-dimensional torus, and let $f:T^r\to T^r$ be
a map.
If $\Per(f)$ denotes the set of periods of $f$, the minimal set
of periods of $f$, denoted by $\MPer(f)$, is defined as
$\bigcap_{g\cong f}\Per(g)$ where $g:T^r\to T^r$ is homotopic to
$f$.
First, we characterize the set $\MPer(f)$ in terms of the
Nielsen numbers of the iterates of $f$.
Second, we distinguish three types of the set $\MPer(f)$ and
show that for each type and any given dimension $r$, the
variation of $\MPer(f)$ is uniformly bounded in a suitable sense.
Finally, we classify all the sets $\MPer(f)$ for self-maps of
the $3$-dimensional torus.