template <class T> line_normal(const Vertex< T, 2 > & v0, const Vertex< T, 2 > & v1) -> Vertex< T, 2 >Rotates line segment by 90 degrees counterclockwise and normalises resulting vector.
template <class Figure> operator<<(std::ostream & out, const Figure & figure) -> std::enable_if< is_figure< Figure >::value, std::ostream & >::type