+template<class T>
+Position<T>
+operator- (Position<T> const & a, Position<T> const & b)
+{
+ return Position<T> (a.x - b.x, a.y - b.y);
+}
+
+template<class T>
+bool
+operator== (Position<T> const & a, Position<T> const & b)
+{
+ return a.x == b.x && a.y == b.y;
+}
+
+template<class T>
+bool
+operator!= (Position<T> const & a, Position<T> const & b)
+{
+ return a.x != b.x || a.y != b.y;
+}
+