See Zagier's paper in the references for a short proof of this fact.

He also gave a short elegant proof of Kruskal's tree theorem.

Because of its importance, its short proof should be noted.

It has a short, elementary proof and was proven in the late 19th century.

It is believed unlikely that a short, simple proof exists.

Brown's short proof was elementary and fully general.

Among his notable achievements was a short and elegant proof of the soul conjecture.

A very short proof does not seem to exist.

This important result is worth a short proof.

Two other short proofs can be found in .