# nLab Strøm's theorem

###### Strøm’s theorem

Let $\left(X,A\right)$ and $\left(Y,B\right)$ be NDR-pairs. Their product in the category of topological pairs

$\left(X×Y,X×B\cup A×Y\right)$(X\times Y,X\times B\cup A\times Y)

is also an NDR-pair.

Revised on December 3, 2009 23:12:57 by Toby Bartels (173.60.119.197)