Three themes in the work of Charles Ehresmann: Local-to-global; Groupoids; Higher dimensions

Abstract

This paper illustrates the themes of the title in terms of: van Kampen type theorems for the fundamental groupoid; holonomy and monodromy groupoids; and higher homotopy groupoids. Interaction with work of the writer is explored.Comment: 13 pages; Expansion of an invited talk given to the 7th Conference on the Geometry and Topology of Manifolds: The Mathematical Legacy of Charles Ehresmann, Bedlewo 8.05.2005-15.05.2005 (Poland) Version 2: corrections of a date and some grammar, slight referencing changes, and a small comment added Version4. Theorem 2.2 got corrected and then uncorrected! It is now corrected. Version5. Reference added. Various minor improvements made in reaction to comment