Ritt called this field the field of "elementary numbers." The term elementary number is also used with
a convention permitting implicit specification, so the two names must be read with
their stated definitions (Chow 1999, p. 442).
Chow, T. Y. "What Is a Closed-Form Number?" Amer. Math. Monthly106, 440-448, 1999.Richardson, D.
"The Elementary Constant Problem." In Proc. Internat. Symp. on Symbolic
and Algebraic Computation, Berkeley, July 27-29, 1992 (Ed. P. S. Wang).
ACM Press, 1992.Ritt, J. Integration
in Finite Terms: Liouville's Theory of Elementary Models. New York: Columbia
University Press, 1948.
of the complex numbers 
which is closed
under exponentiation and logarithms.
