Compact to Hausdorff implies closed
Given: A compact space , a Hausdorff space , a continuous map .
To prove: For any closed subset of , is a closed subset of .
- is compact under the subspace topology: This follows from the given datum that is compact and fact (1).
- is compact under the subspace topology in : First, note that the map is continuous, because it is the composite of the inclusion of in with the map , both of which are continuous. Thus, by fact (2), is compact with the subspace topology from .
- is closed in : This follows from the previous step, the given datum that is Hausdorff, and fact (3).