The main result is that two possible structures which may be imposed on an edge symmetric double category, namely a connection pair and a thin structure, are equivalent. A full proof is also given of the theorem of Spencer, that the category of small 2-categories is equivalent to the category of edge symmetric double categories with thin structure.
Keywords: Double category, 2-category, thin structure, connection.
1991 MSC: 18D05.
Theory and Applications of Categories, Vol. 5, 1999, No. , pp 163-175.
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