Baumslag-Solitar group

A Baumslag-Solitar group is a group with presentation

$$⟨b,t\mid t^{-1}{b}^{m}t=b^n⟩$$

for some non-zero integers $m$ and $n$.

These groups were studied by Baumslag and Solitar[1],who were interested in finding examplesof finitely generated non-Hopfian (http://planetmath.org/HopfianGroup) groups.In particular, the group

$$⟨b,t\mid t^{-1}{b}^{2}t=b^3⟩$$

is non-Hopfian.