The statement and question are in the attachment, thank you

(3) For E/F a Galois extension with G = Gal(E/F) one can define for o ( E two functions, T : E - E and N : E - E as follows: T(a) = g(x) gEG N(a) = 19(0) gCG Show that if o ( E then T(o) ( F and N(o) E F