Abstract In string theory, an important challenge is to show if the singularity of black holes can be smoothed out by complete $$\alpha ^{\prime }$$ α ′ corrections. The simplest case consider a 2D hole or 3D string. This problem was discussed in gauged Wess–Zumino–Witt...

We show that the conformal structure for Riemannian analogues of Kerr black-hole metrics can be given an ambitoric structure. then discuss properties moment maps. In particular, we observe map image is not locally convex near singularity corresponding to ring in interior black hole. proceed classify regular $4$-orbifolds with some completeness assumptions. The tools developed also allow us prov...

We examine the computational complexity of some problems from algebraic automata theory and from the field of communication complexity: testing Green’s relations (relations that are fundamental in monoid theory), checking the property of a finite monoid to have only Abelian subgroups, and determining the deterministic communication complexity of a regular language. By well-known algebraizations...

The hairpin completion is an operation on formal languages which is inspired by the hairpin formation in biochemistry. Hairpin formations occur naturally within DNA-computing. It has been known that the hairpin completion of a regular language is linear context-free, but not regular, in general. However, for some time it is was open whether the regularity of the hairpin completion of a regular ...