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Show that any element of a hereditarily transitive set is hereditarily transitive.

a) Write a proof showing that if x is in a hereditarily transitive set, then every element of x is also in a hereditarily transitive set.
b) Explain the concept of hereditary transitivity without proving the statement.
c) Provide an example of a set that is hereditarily transitive.
d) Disprove the statement by giving a counterexample.

1 Answer

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Final answer:

For a set to be hereditarily transitive, every element within it must be a transitive set. Since every element of a hereditarily transitive set is transitive, and every element within those elements is also transitive, it shows that any element of a hereditarily transitive set is also hereditarily transitive. A counterexample to disprove the statement is not possible, as the statement is correct.

Step-by-step explanation:

Show that any element of a hereditarily transitive set is hereditarily transitive

For a set to be hereditarily transitive, every element of the set must themselves be transitive sets. A transitive set is a set in which every element that is a set is also a subset of the set. To show that any element of a hereditarily transitive set is also hereditarily transitive, consider any element x of a hereditarily transitive set H. Since H is hereditarily transitive, then x must be transitive. For any element y in x, since x is a subset of H, y is also an element of H. As H is hereditarily transitive, y must be transitive as well. Thus, every element of x is transitive, making x a hereditarily transitive set.

Explanation of hereditary transitivity

Hereditary transitivity means that not only is a set transitive, but every set within it is transitive, and this rule applies recursively down to all levels of sets within it.

Example of a set that is hereditarily transitive

An example of a hereditarily transitive set is the set {∅}. The empty set is transitive, and there are no further sets within it to consider, making it trivially hereditarily transitive.

Disproving the statement with a counterexample

statement given cannot be disproven by a counterexample, because it is a correct statement. All elements of a hereditarily transitive set are indeed hereditarily transitive by definition.

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