Some new GP features
bnrinit
This is advantageous when the full bnr would be too costly to
compute
? p = nextprime(2^64);
? \\ bnr = bnrinit(bnf,p); very very slow
? bnr = bnrinit(bnf,p,, (2*3*5*7)^10); \\ fast
? bnr.cyc
%26 = [2100]
? F=bnrclassfield(bnr,3)
%27 = [x^3+55340232221128654887*x
% +333648981822932503936937204063*a]