Arlegi R, Ballester M, Besada M, De Miguel JR, Nieto J, Vázquez CDecember 2007Journal article Journal:Mathematical Social SciencesVolume:54Issue:3, Elsevier, pp.238 - 243No abstract availableKeywords:4904 Pure Mathematics , 49 Mathematical Sciences DOI10.1016/j.mathsocsci.2007.06.004