“…In classical minimum cost spanning tree problems the folk rule is one of the most important rules. It has been studied in several papers, including Bergantiños and Kar (2010), Bergantiños et al ( , 2011Bergantiños et al ( , 2014, Vidal-Puga (2007, 2009), Branzei et al (2004), and Tijs et al (2006).…”