Answer to Question #9298 in Abstract Algebra for John
0. Show that there exist infinitely many finite sets that are not transitive and infinitely man infinite sets that are not transitive.
1. Show: A set X is transitive if and only if X is a subset of P(X).
2. Show: if every X *belongs to* S is transitive, then union(S) is transitive.
3. Show: an ordinal α is a natural number if and only if every nonempty subset of α has a greatest element.
4.Show: If a set of ordinals X does not have a greatest element, then sup X is a limit ordinal.
5. Show: If X is a nonempty set of ordinals, then intersection(X) is an ordinal. Moreover, intersection(X) is the least element of X.
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