1. Notes on a combinatorial theorem of Bohnenblust;Farrell, Roger H.;Duke Math. J.,1965
2. Pure and Applied Mathematics, Vol. XVII;Mitchell, Barry,1965
3. On the foundations of combinatorial theory. I. Theory of Möbius functions;Rota, Gian-Carlo;Z. Wahrscheinlichkeitstheorie und Verw. Gebiete,1964
4. Baxter algebras and combinatorial identities. I, II;Rota, Gian-Carlo;Bull. Amer. Math. Soc. 75 (1969), 325--329; ibid.,1969