ELEMENTARY
↑ Th. Skolem, "Proof of some theorems on recursively enumerable sets", Notre Dame Journal of Formal Logic, 1962, Volume 3, Number 2, pp 65-74, doi:10.1305/ndjfl/1093957149.
1 2 S. A. Volkov, "On the class of Skolem elementary functions", Journal of Applied and Industrial Mathematics, 2010, Volume 4, Issue 4, pp 588-599, doi:10.1134/S1990478910040149.
↑ Volkov, Sergey (2016). "Finite Bases with Respect to the Superposition in Classes of Elementary Recursive Functions [dissertation]". arXiv:1611.04843。