Function: nfeltreduce
Section: number_fields
C-Name: nfreduce
Prototype: GGG
Help: nfeltreduce(nf,a,id): gives r such that a-r is in the ideal id and r
 is small.
Doc: given an ideal \var{id} in
 Hermite normal form and an element $a$ of the number field $\var{nf}$,
 finds an element $r$ in $\var{nf}$ such that $a-r$ belongs to the ideal
 and $r$ is small.