"Generally, you cannot have a straight line in a curved surface (except   
   certain cases, for example a vertical straight line in the surface of a   
   vertical cylinder). Our space is usually curved only a little, so what we call   
   straight lines are not    
   perfectly straight but their deviation from a straight line is negligible for   
   practical purposes."   
      
   Causing no end of problems delivering ordnance in the 17th century, and   
   leading to the discovery of the calculus by both Newton and Leibniz   
   independently, or so the story goes.   
      
   Vive le difference.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)