Knuth's up-arrow notation is a notation invented by Knuth (1976) to represent large numbers in which
evaluation proceeds from the right (Conway and Guy 1996, p. 60):
Conway, J. H. and Guy, R. K. The Book of Numbers. New York: Springer-Verlag, pp. 59-62, 1996.Guy,
R. K. and Selfridge, J. L. "The Nesting and Roosting Habits of the
Laddered Parenthesis." Amer. Math. Monthly80, 868-876, 1973.Knuth,
D. E. "Mathematics and Computer Science: Coping with Finiteness. Advances
in Our Ability to Compute are Bringing Us Substantially Closer to Ultimate Limitations."
Science194, 1235-1242, 1976.Vardi, I. Computational
Recreations in Mathematica. Redwood City, CA: Addison-Wesley, pp. 11
and 226-229, 1991.