Gensler, Orin David. 1993. A Typological Evaluation of Celtic/Hamito-Semitic Syntactic Parallels, PhD. University of California.
p. 4. "prehistoric contact (in the broad sense) does appear to be the most likely way of accounting for the resemblances. I do not believe this claim can be "proven"; I advance it only as the most reasonable way of interpreting the evidence."