Fencing Problem

One day a farmer called up an engineer, a physicist, and a
mathematician and asked them to fence off the largest possible area
with the least amount of fence.

The engineer made the fence in a circle and proclaimed that he had the
most efficient design.

The physicist made a long, straight line and proclaimed, "We can
assume the length is infinite", and pointed out that fencing off half
of the Earth was certainly a more efficient way to do it.

The Mathematician just laughed at them. He built a tiny fence around
himself and said, "I declare myself to be on the outside."