Update theorems/T000871.md

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

Author: GeoffreySangston

theorems/T000871.md

@@ -6,4 +6,5 @@ then:
   P000232: true
 ---
 
-If $V$ is contractible in $U$, then any map $Y \to V$ is null-homotopic in $U$.
+If $V$ is contractible in $U$, any map $Y \to V$ is null-homotopic in $U$.
+Apply this to $Y=S^0, S^1$.