Function: rnfeltup
Section: number_fields
C-Name: rnfelementup
Prototype: GG
Help: rnfeltup(rnf,x): expresses x (belonging to the base field) on the
 relative field.
Doc: $\var{rnf}$ being a relative number
 field extension $L/K$ as output by \kbd{rnfinit} and $x$ being an element of
 $K$ expressed as a polynomial or polmod, computes $x$ as an element of the
 absolute extension $L/\Q$ as a polynomial modulo the absolute equation
 \kbd{\var{rnf}.pol}. If $x$ is given on the integral basis of $K$, apply
 \kbd{nfbasistoalg} first, otherwise PARI will believe you are dealing with a
 vector.
