“…Feltkamp et al (1994) introduced the equal remaining obligation rule, which was studied by Bergantiños and Vidal-Puga (2004, 2007a, and 2007b. This rule belongs to a wide family of rules, introduced by Tijs et al (2006), the family of obligation rules. These rules are defined through Kruskal's algorithm and the philosophy of "construct and charge" (Moretti et al, 2005), i.e., the minimal tree is built arc by arc and the cost of each arc is paid, after its construction, by all the agents who benefit from it.…”