BooksecrCollected Volumepp. xi–xivIntroductionAntonio CampilloUniversidad de Valladolid, SpainMathSciNetzbMATH OpenFranz-Viktor KuhlmannUniversity of Saskatchewan, Saskatoon, CanadazbMATH OpenBernard TeissierInstitut Mathématique de Jussieu-Paris Rive Gauche, FrancezbMATH OpenDownload Chapter PDF