diff --git a/Books/BabyRudin/Chapter02/ex15.cecilia.tex b/Books/BabyRudin/Chapter02/ex15.cecilia.tex new file mode 100644 index 0000000..dc48d31 --- /dev/null +++ b/Books/BabyRudin/Chapter02/ex15.cecilia.tex @@ -0,0 +1,13 @@ +\subsection*{Exercise 15 (Cecilia)} +To show that the theorem is not true for closed subsets, consider the family of set $ \mathbb{N} - \{n\} $ for $ n \in \mathbb{N} $ as subsets of the real number line. + +All the sets are closed because these isolated points have no additional limit points. (i.e any points that is not a natural number will have a neighborhood that does not intersect with the set.) +Any finite intersection is not empty because there is a maximum number that is being deleted by the sets, and the number after it is not deleted by any set and therefore belong to the intersection. +But the infinite intersection is empty because there is no maximum number that is not deleted by any set. + +To show that the theorem is not true for bounded subsets, consider the family of set $ [1, 2] $ with $ r $ deleted for all real numbers $ r $. + +All the sets are bounded because they are all subsets of $ [1, 2] $. +Any finite intersection is not empty because there are infinitely many real numbers in $ [1, 2] $ but we only deleted a finite number of them, so there must be a number that is not deleted. +But the infinite intersection is empty because we deleted all the real numbers in $ [1, 2] $. +