Update theorems/T000847.md

Co-authored-by: Geoffrey Sangston <geoffreysangston@gmail.com>

Author: prabau

theorems/T000847.md

@@ -8,5 +8,5 @@ then:
 
 For each $x\in X$, every neighborhood of $x$ contains an open neighborhood homeomorphic to
 some Euclidean space $\mathbb R^n$ or some closed half-space $\mathbb R^n_+$.
-And $\mathbb R^n$ and $\mathbb R^n_+$ are both {P199}
+And both $\mathbb R^n$ and $\mathbb R^n_+$ are {P199}
 as they can be deformation retracted to a point using a straight-line homotopy.