The Baire Category Theorem Review

The Baire Category Theorem Review

We will now review some of the recent material regarding the Baire Category theorem.

  • On The Cantor Intersection Theorem for Complete Metric Spaces page we looked at the Cantor intersection theorem which states the following. If $X$ is a complete metric space and if $(x_n)_{n=1}^{\infty}$ is a sequence of points in $X$ and $(r_n)_{n=1}^{\infty}$ is a sequence of positive real numbers such that $\displaystyle{\lim_{n \to \infty} r_n = 0}$ and:
(1)
\begin{align} \quad ... \overline{B}(x_{n+1}, r_{n+1}) \subseteq \overline{B}(x_n, r_n) \subseteq ... \subseteq \overline{B} (x_1, r_1) \end{align}
  • Then there exists exactly one point $x \in X$ such that:
(2)
\begin{align} \quad \bigcap_{n=1}^{\infty} \overline{B}(x_n, r_n) = \{ x \} \end{align}
  • On The Baire Category Theorem for Complete Metric Spaces page we looked at another important theorem called the Baire category theorem which states the following. If $X$ is a complete metric space and if $(D_n)_{n=1}^{\infty}$ is a countable collection of open and ##gold|dense#3 sets in $X$ then the intersection:
(3)
\begin{align} \quad \bigcap_{n=1}^{\infty} D_n \end{align}
  • Is dense in $X$.
(4)
\begin{align} \quad \bigcup_{n=1}^{\infty} F_n \end{align}
  • Has empty interior.
Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License