property describes the cartesian product X x Y uniquely
| (up to a bijection);  the same diagram, read in the category
| of topological spaces or of groups, describes uniquely the
| cartesian product of spaces or the direct product of groups.
|
| Mac Lane, 'Cat Work Math', pages 1-2.
|
| Saunders Mac Lane,
|'Categories for the Working Mathematician',
| Springer-Verlag, New York, NY, 1971.

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