title: What is lhs/rhs and how is it being used in this program?
body: <pre><code>struct Point2D {
  float x;
  float y;
  };
  
  Point2D operator+(Point2D lhs, Point2D rhs);
  Point2D operator-(Point2D lhs, Point2D rhs);
  Point2D operator*(Point2D lhs, Point2D rhs);
  Point2D operator/(Point2D lhs, Point2D rhs);
  </code></pre>
  
  <p>Also, what is 'operator' and what is it's role?</p>