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Abelian Cover


An Abelian cover of a group G is a collection of subgroups that are Abelian and whose union is G. Let a(G) be the least size of such a cover and let omega(G) be the largest size of a set of pairwise noncommuting group elements. For a non-Abelian group, these are respectively the chromatic number and clique number of its noncommuting graph (Lecomte 2026).

Lecomte (2026) proved that

 sup_(omega(G)<=n)a(G)=2^(|_(n-1)/2_|)+1

for every integer n>=63, where |_x_| is the floor function and the supremum ranges over all groups. Writing m=|_(n-1)/2_|, a group with omega(G)<=n attains equality precisely when G^'=C_2 and G/Z(G)=GF(2)^(2m), where G^' is the commutator subgroup and Z(G) is the group center. Here C_2 is the cyclic group of order two and GF(2) is the finite field with two elements. Lecomte (2026) acknowledges ChatGPT and Aristotle assistance with exploratory proof checking and consistency review.


See also

Abelian Group, Group, Noncommuting Graph

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References

Lecomte, G. "Eventual Exactness and Rigidity for Abelian Covers of Groups." 12 Oct 2026. https://arxiv.org/abs/2610.22388.

Cite this as:

Weisstein, Eric W. "Abelian Cover." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/AbelianCover.html

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