The volume of a differentiable stack (Q844118)

The notion of cardinality of a discrete groupoid is generalized to Lie groupoids. The cardinality of a groupoid was defined by \textit{J. C. Baez} and \textit{J. Dolan} in [Mathematics unlimited, 29--50 (2001; Zbl 1004.18001)] to be sum of orders of isotropy groups. Here, this is extended to Lie groupoids and their associated smooth stalks considering the cardinality as a geometric rather than topological quantity and this extended notion is called volume of stalk which reduces to that of the cited paper in the discrete case.