Author: Urs Format: MarkdownItexadded to _[[invariant]]_ a section, [here](http://ncatlab.org/nlab/show/invariant#ViaSectionsOfActionGroupoidProjections), with detailed exposition of how invariants are equivalently sections of the action groupoid projection
added to invariant a section, here, with detailed exposition of how invariants are equivalently sections of the action groupoid projection