5 | Closed Sets, Interior, Closure, Boundary
www.math.buffalo.edu › ~badzioch › MTH427Boundary 5.1 Definition. Let Xbe a topological space. A set A⊆Xis a closed set if the set XrAis open. 5.2 Example. A closed interval [a;b] ⊆R is a closed set since the set Rr[a;b] = (−∞;a)∪(b;+∞) is open in R. 5.3 Example. Let T Zabe the Zariski topology on R. Recall that U∈T Zaif either U= ? or U= RrS where S⊂R is a finite set. As a consequence closed sets in the Zariski topology are the whole space
Boundary (topology) - Wikipedia
https://en.wikipedia.org/wiki/Boundary_(topology)The boundary of a set is equal to the boundary of the set's complement: A set is a dense open subset of if and only if The interior of the boundary of a closed set is the empty set. Consequently, the interior of the boundary of the closure of a set is the empty set. The interior of the boundary of an open set is also the empty set. Consequently, the interior of the …