On projections of the tails of a power

Samuel M. Corson, Saharon Shelah

Published 2022-11-24Version 1

Let $\kappa$ be an inaccessible cardinal, $\mathfrak{U}$ be a universal algebra, and $\sim$ be the equivalence relation on $\mathfrak{U}^{\kappa}$ of eventual equality. From mild assumptions on $\kappa$ we give general constructions of $\mathcal{E} \in End(\mathfrak{U}^{\kappa}/\sim)$ satisfying $\mathcal{E} \circ \mathcal{E} = \mathcal{E}$ which do not descend from $\Delta \in End(\mathfrak{U}^{\kappa})$ having small strong supports. As an application there exists an $\mathcal{E} \in End(\mathbb{Z}^{\kappa}/\sim)$ which does not come from a $\Delta \in End(\mathbb{Z}^{\kappa})$.