The maximum commutative subsemigroup conjecture for full transformation semigroups

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Let XX be a set, and let T(X)\mathcal{T}(X) denote the full transformation semigroup on XX. For the notation Nx1,,xtXN^{X}_{x_1,\ldots,x_t} and the functions ξ\xi and α\alpha, use the definitions introduced in the paper. Maximum commutative subsemigroup conjecture. Suppose that X7|X|\geqslant 7. Then the maximum size of a commutative subsemigroup of T(X)\mathcal{T}(X) is (X)ξ+1(|X|)\xi+1. Moreover, the maximum-order commutative subsemigroups of T(X)\mathcal{T}(X) are precisely the semigroups

Nx1,,xtX{idX},N^{X}_{x_1,\ldots,x_t}\cup\{\operatorname{id}_{X}\},

where t=(X)αt=(|X|)\alpha and x1,,xtXx_1,\ldots,x_t\in X are pairwise distinct. This conjecture would resolve the open problem of determining and characterizing the largest commutative subsemigroups of the full transformation semigroup, and would consequently provide information about the corresponding clique-number problems.

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Primary source

Tânia Paulista, “Characterizing the largest commutative (full and partial) transformation semigroups of certain types”, arXiv:2511.09495 (2025).

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