It is the algebraic extension
It should be:
Fernando Revilla
Possibly you meant instead of
Fernando Revilla
" " can also be expressed as "the smallest field containing all rational numbers and ". It can be shown that all such numbers are of the form for some rational numbers p and q.
and that is as far as it can be factored in Q or, for that matter, .
However,
which are in
So: in but in .