Answer to Question #282266 in Differential Geometry | Topology for Natasha

Question

DG. Let X be the universal space. Which set is equal to $\mathrm{Cl}(X) \cap \mathrm{Cl}(X \backslash A) ?(\mathrm{Fr}$ stands for the boundary of a set, $\mathrm{Cl}$ means the closure of a set).

Answer 1

Solution:

X is a universal set. So, CI(X) = X.

Then,

$CI(X)\cap CI(X / A) \\=X \cap CI(X / A) \\= CI(X / A)$