18 references, page 1 of 2 1. M. Abert, A. Jaikin-Zapirain, and N. Nikolov, The rank gradient from a combinatorial viewpoint, Groups Geom. Dyn. 5 (2011), 213-230.

2. M. Abert and N. Nikolov, Rank gradient, cost of groups and the rank versus Heegaard genus problem, J. Eur. Math. Soc. (2012), no. 14, 1657-1677.

3. B. Bekka, P. de la Harpe, and A. Valette, Kazhdan's property (T), New Mathematical Monographs, no. 11, Cambridge University Press, 2008.

4. D. E. Cohen, Subgroups of HNN groups, J. Aust. Math. Soc. 17 (1974), no. 4, 394-405.

5. D. Gaboriau, Cout des relations dequivalence et des groupes, Invent. Math. (2000), no. 139, 41-98.

6. , Invariants L2 de relations d'equivalence et de groupes, Publ. Math. Inst. Hautes. Etudes. Sci. 95 (2002), 93-150.

7. A. Kar and N. Nikolov, Rank gradient for Artin groups and their relatives, arXiv:1210.2873v3 (2012).

8. M. Lackenby, Expanders, rank and graphs of groups, Israel J. Math. 146 (2005), no. 1, 357-370.

9. , Large groups, property (τ ) and the homology growth of subgroups, Math. Proc. Camb. Phil. Soc. 146 (2009), 625-648.

10. M. Zero´n-Medina Laris, Positive rank gradient and p-largeness for groups definied by presentations with pdeficiency less than or equal to one, arXiv:1306.2467v1 (2013).