  We introduce orbifolds from the classical point of view, using charts, and
present orbifold versions of elementary objects from Algebraic Topology, such
as the fundamental group, coverings and Euler characteristic; Differential
Topology/Geometry, including orbibundles, differential forms, integration and
(equivariant) De Rham cohomology; and Riemannian Geometry, surveying
generalizations of classical theorems to this setting.
