© 1995 by London Mathematical Society
© The London Mathematical Society
Extensions of Asymptotic Fields Via Meromorphic Functions
University of Kent at Canterbury Canterbury, Kent CT2 7NF
Received 29 April 1992. Revision received 21 March 1994.
An asymptotic field is a special type of Hardy field in which, modulo an oracle for constants, one can determine asymptotic behaviour of elements. In a previous paper, it was shown in particular that limits of real Liouvillian functions can thereby be computed. Let
denote an asymptotic field and let f
. We prove here that if G is meromorphic at the limit of f (which may be infinite) and satisfies an algebraic differential equation over R(x), then
(G o f) is an asymptotic field. Hence it is possible (modulo an oracle for constants) to compute asymptotic forms for elements of
(G o f). An example is given to show that the result may fail if G has an essential singularity at lim f.