1. C.A. Alfaro, The sandpile group of a multigraph, Master thesis, Mathematics Department, Cinvestav-IPN, February 2010.
2. On the critical group of the n-cube;Bai;Linear Algebra Appl.,2003
3. Self-organized criticality: an explanation of the 1/f noise;Bak;Phys. Rev. Lett.,1987
4. Self-organized criticality;Bak;Phys. Rev. A,1988
5. Harmonic morphims and hyperelliptic graphs;Baker;Internat. Math. Res. Notices,2009