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

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

Double groupoids, matched pairs and then matched triples

In this note we show that the known relation between double groupoids and matched pairs of groups may be extended, or seems to extend, to the triple case. The references give some other occurrences of double groupoids.Comment: 5 page