- #1
ArcanaNoir
- 779
- 4
Homework Statement
I am working on the proof that taking closure and interior of a set in a metric space can produce at most 7 sets. The piece I need is that [itex] \bar{\mathring{A}} = \bar{\mathring{\bar{\mathring{A}}}} [/itex].
Homework Equations
Interior of A is the union of all open sets contained in A, aka the largest open set contained in A.
Closure of A is the intersection of all closed sets containing A, aka the smallest closed set containing A.
The Attempt at a Solution
[itex] \bar{\mathring{A}}[/itex] is a closed set. [itex]\mathring{\bar{\mathring{A}}}\subseteq \bar{\mathring{A}}[/itex]. Since [itex]\bar{\mathring{\bar{\mathring{A}}}} [/itex] is the smallest closed set containing [itex] \mathring{\bar{\mathring{A}}} [/itex] we have that [itex]\bar{\mathring{\bar{\mathring{A}}}}\subseteq \bar{\mathring{A}}[/itex].
I'm not sure how to get the inclusion [itex] \bar{\mathring{A}}\subseteq \bar{\mathring{\bar{\mathring{A}}}} [/itex]
Last edited: