1. Baudisch, A.: Subgroups of Semifree Groups. Akademie der Wissenschaften der DDR Zentralinstitutfur Mathematik und Mechanik (1979)
2. Bridson, M.: A condition that prevents groups from acting nontrivially on trees. The Zieschang Gedenkschrift. Geom. Topol. Monogr. 14, 129–133 (2008)
3. Bridson, M.R., Haefliger, A.: Metric Spaces of Non-positive Curvature. Grundlehren der Mathematischen Wissenschaften [Fundamental Principles of Mathematical Sciences], vol. 319. Springer, Berlin (1999)
4. Charney, R., Ruane, K., Stambaugh, N., Vijayan, A.: The automorphism group of a graph product with no SIL. Ill. J. Math. 54(1), 249–262 (2010)
5. Clay, M., Margalit, D. (eds.): Office Hours with a Geometric Group Theorist. Princeton University Press, Princeton, NJ (2017)