Bächle, A., Janssens, G., Jespers, E., Kiefer, A., & Temmerman, D. (2022). A dichotomy for integral group rings via higher modular groups as amalgamated products. Journal of Algebra, 604(1), 185-223. https://doi.org/10.1016/j.jalgebra.2022.03.044 (Original work published 2022)