Building a fence

One day a farmer called up an engineer, a physicist, and a mathematician and asked them to fence of 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 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."