An engineer, a physicist and a mathematicians have to build a fence 
around a large flock of sheep, using as little material as possible. 

The engineer forms the flock into a circular shape and constructs a 
fence around it. 

The physicist builds a fence with an infinite diameter and pulls it 
together until it fits around the flock. 

The mathematicians thinks for a while, then builds a fence around 
himself and defines himself as being outside.