On the Isomorphism of Some One-Relator Groups
  A class of one-relator groups such that every group in the class is determined by a triple of integers and is an HNN-extension of some Baumslag -- Solitar group is considered. A criterion for two groups in this class to be isomorphic and criterion for two non-isomorphic groups to be a homomorphic image of each other are obtained. This result leads to a negative answer to the question 3.33 from "Kourovka Notebook". 
A.V.Borschev, D.I.Moldavanskii