Geodesic
Proof of a generalization of the conjecture of Hanna Neumann for virtually free groups
Sbornik. Mathematics, Tome 187 (1996) no. 10, pp. 1561-1575 
Yu. S. Semenov. Proof of a generalization of the conjecture of Hanna Neumann for virtually free groups. Sbornik. Mathematics, Tome 187 (1996) no. 10, pp. 1561-1575. http://geodesic.mathdoc.fr/item/SM_1996_187_10_a7/
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     title = {Proof of a~generalization of the~conjecture of {Hanna} {Neumann} for virtually free groups},
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Voir la notice de l'article provenant de la source Math-Net.Ru

The article confirms a generalization of a conjecture of Hanna Neumann for groups having the free product of three groups of order 2 as subgroups of finite index.

[1] Semenov Yu. S., “Rings associated with hyperbolic groups”, Comm. Algebra, 22 (15) (1994), 6323–6347 | DOI | MR | Zbl

[2] Neumann W., “On intersections of finitely generated subgroups of free groups”, Lecture Notes in Math., 1456, 1990, 161–170 | MR | Zbl

[3] Neumann H., “On intersections of finitely generated subgroups of free groups”, Publ. Math. Debrecen, 4 (1955–56), 186–189 ; 5 (1957–58), 128 | MR | MR | Zbl