G. R. Blakley and I. Borosh, Knuth's iterated powers, Advances in Mathematics, vol.34, issue.2, pp.109-136, 1979.
DOI : 10.1016/0001-8708(79)90052-5

URL : http://doi.org/10.1016/0001-8708(79)90052-5

D. E. Knuth, Mathematics and Computer Science: Coping with Finiteness, Science, vol.194, issue.4271, pp.1235-1242, 1976.
DOI : 10.1126/science.194.4271.1235

V. Blondel, Properties of a hierarchy of operations on binary trees

V. Blondel, Une famille d'opérations sur les arbres binaires, C. R. Acad. Sci. Paris, Série, vol.1, issue.321, pp.491-494, 1995.

D. E. Knuth, Semantics of context-free languages, Mathematical Systems Theory, vol.9, issue.2, pp.127-145, 1968.
DOI : 10.1007/BF01692511