A categorical proof of the statement given by the title is provided, in generalization of a result for topological spaces proved recently by Clementino, Hofmann and Tholen.
Keywords: proper map, separated map, perfect map, quotient map, exponentiable map.
2000 MSC: 18A20, 18B30, 54C10.
Theory and Applications of Categories, Vol. 8, 2001, No. 16, pp 457-464.
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