Geodesic
A homotopy double groupoid of a Hausdorff space
Theory and applications of categories, Tome 10 (2002), pp. 71-93

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We associate to a Hausdorff space, $ X $, a double groupoid, $ \mbox{\boldmath $ \rho $}^{\square}_{2} (X) $, the homotopy double groupoid of $ X $. The construction is based on the geometric notion of thin square. Under the equivalence of categories between small $ 2 $-categories and double categories with connection the homotopy double groupoid corresponds to the homotopy 2- groupoid, $ {\bf G}_{2} (X) $. The cubical nature of $ \mbox{\boldmath $ \rho $}^{\square}_{2} (X) $ as opposed to the globular nature of $ {\bf G}_{2} (X) $ should provide a convenient tool when handling `local-to-global' problems as encountered in a generalised van Kampen theorem and dealing with tensor products and enrichments of the category of compactly generated Hausdorff spaces.

Classification : 18D05, 20L05, 55Q05, 55Q35.
Keywords: double groupoid, connection, thin structure, 2-groupoid, double track, 2- track, thin square, homotopy addition lemma. 
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     title = {A homotopy double groupoid of a {Hausdorff} space},
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     year = {2002},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/TAC_2002_10_a1/}
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Ronald Brown; Keith A. Hardie; Klaus Heiner Kamps; Timothy Porter. A homotopy double groupoid of a Hausdorff space. Theory and applications of categories, Tome 10 (2002), pp. 71-93. http://geodesic.mathdoc.fr/item/TAC_2002_10_a1/