Hochschild homology invariants of K\"ulshammer type of derived categories

For a perfect field $k$ of characteristic $p>0$ and for a finite dimensional symmetric $k$-algebra $A$ K\"ulshammer studied a sequence of ideals of the centre of $A$ using the $p$-power map on degree 0 Hochschild homology. In joint work with Bessenrodt and Holm we removed the condition to be symmetric by passing through the trivial extension algebra. If $A$ is symmetric then the dual to the K\"ulshammer ideal structure was generalised to higher Hochschild homology in earlier work. In the present paper we follow this program and propose an analogue of the dual to the K\"ulshammer ideal structure on the degree $m$ Hochschild homology theory also to not necessarily symmetric algebras

A short proof of Halin’s grid theorem

We give a short proof of Halin’s theorem that every thick end of a graph contains the infinite grid