truncate

Given a map, is it possible to extract a map with only low order terms?

If I have:
ring r = real,(x,y,z),dp;
map f=r,x3+x2+x3y+4;

I want to get for instance
x2+4

Thanks,
Riccardo

Yes, jet provides this functionality:
ring r = real,(x,y,z),dp;
map f=r,x3+x2+x3y+4;
jet(ideal(f),2);
-> _[1]=x2+4.000e+00
and to a map again:
map ff=r,jet(ideal(f),2);