Calkin, N. and Wilf, H. S. "Recounting the Rationals." Amer. Math. Monthly107, 360-363, 2000.Dijkstra, E. W.
Selected
Writings on Computing: A Personal Perspective. New York: Springer-Verlag,
pp. 215-232, 1982.Gibbons, L.; Lester, D.; and Bird, R. "Functional
Pearl: Enumerating the Rationals." J. Func. Prog.16, 281-291,
2006.Sloane, N. J. A. Sequence A002487/M0141
in "The On-Line Encyclopedia of Integer Sequences."