Covering space semigroups and retracts of compact Lie groups

@article{Hofmann2016CoveringSS,
title={Covering space semigroups and retracts of compact Lie groups},
author={K. Hofmann and J. Martin},
journal={Journal of Geometry},
year={2016},
volume={107},
pages={427-439}
}

If B is a compact connected Lie group and N a finite central subgroup, let $${f\colon B\to B/N}$$f:B→B/N be the associated covering morphism. The mapping cylinder $${{\mathrm{MC}}(f)}$$MC(f) is a compact monoid which we call a covering space semigroup. A prominent example is the classical Möbius band $${\mathbb{M}^2}$$M2. An (L)-semigroup is a compact n-manifold X with connected boundary B together with a monoid structure on X such that B is a subsemigroup of X. Every covering space semigroup… Expand