Update properties/P000087.md

Co-authored-by: Patrick Rabau <70125716+prabau@users.noreply.github.com>

Author: GeoffreySangston

properties/P000087.md

@@ -8,7 +8,7 @@ refs:
     name: Topology (Munkres)
 ---
 
-$X$ is homeomorphic to a topological group.
+$X$ is homeomorphic to a [topological group](https://en.wikipedia.org/wiki/Topological_group).
 
 Equivalently, there exists a continuous group operation $(x,y)\mapsto x\cdot y$ on $X$ such that
 the inverse operation $x\mapsto x^{-1}$ is also continuous.