Function: nfeltispower
Section: number_fields
C-Name: nfispower
Prototype: lGGLD&
Help: nfeltispower(nf,x,n,{&y}): returns 1 if x is an n-th power in nf (and set y to
 an n-th root if present), else returns 0.
Doc: returns $1$ if $x$ is an $n$-th power in the number field \kbd{nf} (and sets $y$ to an $n$-th root if the
 argument is present), else returns 0.

 \bprog
 ? nf = nfinit(1+x^2);
 ? nfeltispower(nf, -4, 4, &y)
 %2 = 1
 ? y
 %3 = [-1, -1]~
 @eprog
