Matrix theoretic interpretation of the classical Markoff theory. (L'interprétation matricielle de la théorie de Markoff classique.) Perrine, Serge (2002) International Journal of Mathematics and Mathematical Sciences
Moduli of graphs and automorphisms of free groups. K. Vogtmann, M. Culler (1986) Inventiones mathematicae
Morita classes in the homology of automorphism groups of free groups. Conant, James, Vogtmann, Karen (2004) Geometry & Topology