1. R. Ayala, L.M. Fernández and J.A. Vilches, Critical elements of proper discrete Morse functions. Mathematica Pannonica, 19(2) (2008), 171–185.
2. R. Ayala, L.M. Fernández and J.A. Vilches, Desigualdades de Morse generalizadas sobre grafos, Actas de las III Jornadas de Matemática Discreta y Algorítmica, Universidad de Sevilla, Sevilla, (2002), 159–164.
3. R. Ayala, L.M. Fernández and J.A. Vilches, Morse inequalities on certain infinite 2-complexes. Glasgow Math. J., 49 (2007), 155–165.
4. R. Forman, Combinatorial Differential Topology and Geometry. New Perspectives in Geometric Combinatorics, MSRI Publications, 38 (1999), 177–206.
5. R. Forman, Morse Theory for cell complexes. Adv. in Math., 134(1) (1998), 90–145.