Bourbaki

Exercise 19, § 2

Tag 03UT, permanent. Cite it as [Bourbaki, Tag 03UT].

Theory of Sets, III, 228

It is set in small type as supplementary.

Let α\alpha and β\beta be two ordinals, and let E, F be two well-ordered sets such that Ord⁡(E)=α\operatorname{Ord}(E)=\alpha and Ord⁡(F)=β\operatorname{Ord}(F)=\beta. In the set EFE^F of mappings of F into E, consider the subset G of mappings gg such that g(y)g(y) is equal to the least element of E for all but a finite number of elements y∈Fy\in F. If F∗F^* is the ordered set obtained by endowing F with the opposite order, show that G is a connected component with respect to the relation “xx and yy are comparable” (Chapter II, § 6, Exercise 10) in the product EF∗E^{F^*} endowed with the ordering defined in Exercise 12, and show that G is well-ordered. Furthermore, prove that Ord⁡(G)=αβ\operatorname{Ord}(G)=\alpha^\beta (use the uniqueness property of Exercise 17 (b)).

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