Function: rnfdisc
Section: number_fields
C-Name: rnfdiscf
Prototype: GG
Help: rnfdisc(nf,T): given a polynomial T with coefficients in nf, gives a
 2-component vector [D,d], where D is the relative ideal discriminant, and d
 is the relative discriminant in nf^*/nf*^2.
Doc: given an \var{nf} structure attached to a number field $K$, as output
 by \kbd{nfinit}, and a monic irreducible polynomial $T\in K[x]$ defining a
 relative extension $L = K[x]/(T)$, compute the relative discriminant of $L$.
 This is a vector $[D,d]$, where $D$ is the relative ideal discriminant and
 $d$ is the relative discriminant considered as an element of $K^*/{K^*}^2$.
 The main variable of $\var{nf}$ \emph{must} be of lower priority than that of
 $T$, see \secref{se:priority}.

 \misctitle{Huge discriminants, helping rnfdisc} the format $[T,B]$ is
 also accepted instead of $T$ and computes an order which is maximal at all
 $p < B$, see \kbd{??rnfinit}: the valuation of $D$ is then correct at all
 prime ideals $\goth{p}$ above a rational prime $p < B$ but may be incorrect
 at other primes.
