Let $G$ be a group acting on some set $\Omega$. Just a minor point, but saying that some nontrivial element $g \in G$ acts semi-regularly, does this mean that $g$ itself has no fixed point, or that the subgroup generated by $g$ has trivial point stabilizers for each point? I guess the latter, but just to confirm my guess I am asking.
2026-04-03 00:19:32.1775175572
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What does it mean to say a single element acts semi-regularly
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A group $G$ acts semiregularly on a set $X$, if it acts freely, i.e., for $g\in G$, if there exists an $x$ in $X$ with $g.x = x$ (that is, if $g$ has at least one fixed point), then $g$ is the identity. There are several types of group actions, e.g., see here.
The usual definition I've seen is that an element is said to be semiregular (or act semiregularly) if it generates a semiregular subgroup. It is not hard to see that this is equivalent to the element having all cycles of the same length, when written as a product of disjoint cycles.