2 added 111 characters in body

Another nice reference (with a short proof) isin

G. Greiter, A simple proof for a theorem of Kronecker, Amer. Math. Monthly 85 (1978), no. 9, 756–757.

The proof in this paper is related to the proofs given above by Kevin and David, but is a bit more elementary.

1

Another nice reference (with a short proof) is in

G. Greiter, A simple proof for a theorem of Kronecker, Amer. Math. Monthly 85 (1978), no. 9, 756–757.