Geodesic
Coinitial Grapfis and Whitehead Automorphisms
Canadian journal of mathematics, Tome 31 (1979) no. 1, pp. 112-123

Voir la notice de l'article provenant de la source Cambridge University Press

Coinitial graphs were used in [2; 3 ; 4] as a combinatorial tool in the Reidemeister- Schreier process in order to prove subgroup theorems for Fuchsian groups. Whitehead had previously introduced such graphs but used topological methods for his proofs [8; 9]. Subsequently Rapaport [7] and Iliggins and Lyndon [1] gave algebraic proofs of the results in [9], and AIcCool [5; 6] has further developed these methods so that presentations of automorphism groups could be found.In this paper it is shown that Whitehead automorphisms can be described by a “cutting and pasting” operation on coinitial graphs. Section 1 defines and gives some combinatorial properties of these operations, based on [1]. 
Hoare, A. H. M. Coinitial Grapfis and Whitehead Automorphisms. Canadian journal of mathematics, Tome 31 (1979) no. 1, pp. 112-123. doi: 10.4153/CJM-1979-012-x
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