## Closed Sets and Limit Points

Definition (Closed) A subset $A$ of a topological space $X$ is said to be closed if the set $X-A$ is open.
Definition (Product Topology on $X \times Y$) Let $(X,\mathfrak{T}_X)$ and $(Y,\mathfrak{T}_Y)$ be topological spaces. The product space topology on \$X\times...