Einstein, A. and Kaufman, B., A new form of the general relativistic field equations. Ann. of Math. (2) 1955, 62, 128--138.

Gillis, J. Kaufman, B., The stability of a rotating viscous jet. Quart. Appl. Math. 1962, 19, 301--308.

Gillis, J. Zeilberger, D. A direct combinatorial proof of a positivity result. European Journal of Combinatorics, 1983, 4, no. 3, 221--223.

Doron Zeilberger's Home Page