The eventual 8g conjecture for purely non-free actions

From papers

Let μ(g)\mu(g) be the maximum order of a purely non-free (gpnf) action on a closed orientable surface of genus gg. For even g2g\geq 2, the paper proves that either μ(g)=8g\mu(g)=8g or

μ(g)=8nn4(g1)\mu(g)=\frac{8n}{n-4}(g-1)

for some integer n>4n>4, and that the latter case occurs for only finitely many gg for each fixed nn.

Eventual 8g conjecture.

μ(g)=8g\mu(g)=8g

for all but finitely many gg. The authors additionally suggest that this may hold for all gg. The preceding results leave open whether infinitely many values of nn can produce the exceptional form; this conjecture asserts that such exceptions occur only finitely often overall.

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Sources & referencesView supporting material

Primary source

C. Bagiński, G. Gromadzki and R. A. Hidalgo, “On the biggest purely non-free conformal actions on compact Riemann surfaces and their asymptotic properties”, arXiv:2605.04214 (2026).

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