Rational subsets of unitriangular groups
Markus Lohrey · International Journal of Algebra and Computation · 2015
It is shown that there exist d, ℓ ≥ 3 and a sequence C1, …, Cℓ of cyclic subgroups of the d-dimensional unitriangluar matrix group over ℤ (which is finitely generated nilpotent) such that membership in the product C1 C2 ⋯ Cℓ is undecidable.