L' inj enuit m eme d' un regard neuf (celui de la science l'est toujours) peut parfois clairer d' un jour nouveau d' anciens probl emes. J.Monod 77, p. 13] his book is intended as a comprehensive introduction to the theory of T principalsheaves andtheirconnections inthesettingofAbstractDi?- ential Geometry (ADG), the latter being initiated by A. Mallios'sGeometry of Vector Sheaves 62]. Based on sheaf-theoretic methods and sheaf - homology,...