We have received a personal communication, dated May 3rd, 1995, from F. Galvin, who kindly informs us that he did not prove such a result, and that he is not aware of the existence of a proof.
It thus seems uncertain if a proof of this statement has ever been published, and it is possible that such a proof has not been found.
May 15, 1995. T.R. Jensen and B. Toft.