3 papers
math.GR2022
Pointlike sets with respect to ER
Karsten Henckell, Samuel Herman
We show that pointlike sets are decidable for the pseudovariety of finite semigroups whose idempotent-generated subsemigroup is R-trivial. Notably, our proof is constructive: we pr…
math.GR2021
Product Expansions Redux
Karsten Henckell, Samuel Herman
We introduce a generalization of the product expansion of a finite semigroup. As an application, we provide an alternative proof of the decidability of pointlike sets for pseudovar…
math.GR2021
A General Theory of Pointlike Sets
Karsten Henckell, Samuel Herman
We introduce a general unifying framework for the investigation of pointlike sets. The pointlike functors are considered as distinguished elements of a certain lattice of subfuncto…