Algebra in superextensions of groups, I: zeros and commutativity

T. Banakh ; V. Gavrylkiv ; O. Nykyforchyn

Algebra and discrete mathematics, no. 3 (2008), pp. 1-29.

Résumé

Given a group $X$ we study the algebraic structure of its superextension $\lambda (X)$. This is a right-topological semigroup consisting of all maximal linked systems on $X$ endowed with the operation $$ \mathcal A\circ\mathcal B=\{C\subset X:\{x\in X:x^{-1}C\in\mathcal B\}\in\mathcal A\} $$ that extends the group operation of $X$. We characterize right zeros of $\lambda (X)$ as invariant maximal linked systems on $X$ and prove that $\lambda (X)$ has a right zero if and only if each element of $X$ has odd order. On the other hand, the semigroup $\lambda (X)$ contains a left zero if and only if it contains a zero if and only if $X$ has odd order $|X|\le 5$. The semigroup $\lambda (X)$ is commutative if and only if $|X|\le 4$. We finish the paper with a complete description of the algebraic structure of the semigroups $\lambda (X)$ for all groups $X$ of cardinality $|X|\le 5$.

Détail

Mots-clés : Superextension, right-topological semigroup.