@article{10_4171_ggd_357,
     author = {David El-Chai Ben-Ezra},
     title = {The congruence subgroup problem for the free metabelian group on two generators},
     journal = {Groups, geometry, and dynamics},
     pages = {583--599},
     year = {2016},
     volume = {10},
     number = {2},
     doi = {10.4171/ggd/357},
     url = {http://geodesic.mathdoc.fr/articles/10.4171/ggd/357/}
}