Compactness Properties Preserved under Projection Mapping

Theorem
Let $\left \langle {\left({X_\alpha, \vartheta_\alpha}\right)}\right \rangle$ be a sequence of topological spaces.

Let $\displaystyle \left({X, \vartheta}\right) = \prod \left({X_\alpha, \vartheta_\alpha}\right)$ be the product space of $\left \langle {\left({X_\alpha, \vartheta_\alpha}\right)}\right \rangle$.

Let $\operatorname{pr}_\alpha: \left({X, \vartheta}\right) \to \left({X_\alpha, \vartheta_\alpha}\right)$ be the projection on the $\alpha$ coordinate.

Then $\operatorname{pr}_\alpha$ preserves the following compactness properties.

That is, if $\left({X, \vartheta}\right)$ has one of the following properties, then each of $\left({X_\alpha, \vartheta_\alpha}\right)$ has the same property.


 * Compactness


 * Sigma-Compactness


 * Countable Compactness


 * Sequential Compactness


 * Lindelöf Space


 * Local Compactness


 * Paracompactness

Proof
First note that Projection from Product Topology is Continuous.

It follows from Compactness Properties Preserved under Continuous Mappings, we have that:


 * Compactness
 * Sigma-Compactness
 * Countable Compactness
 * Sequential Compactness
 * Lindelöf Space

are all preserved under projections.

Next note that Projection from Product Topology is Open.

It follows from Local Compactness Preserved under Open Continuous Mappings that local compactness is preserved under projections.

The final result is that Paracompactness Preserved under Projections.