Update properties/P000087.md

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

Author: GeoffreySangston

properties/P000087.md

@@ -10,7 +10,7 @@ refs:
 
 $X$ is homeomorphic to a topological group.
 
-Equivalently, there exists a continuous group operation $(x,y)\mapsto x\cdot y$ on the space such that
+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.
 
 Contrary to Munkres or Willard, we do not assume any separation axiom like {P3}, {P2} or {P1}.