Section InfinitePrimitiveElementTheorem.
Local Notation "p ^ f" := (map_poly f p) : ring_scope.
Variables (F L : fieldType) (iota : {rmorphism F -> L}).
Variables (x y : L) (p : {poly F}).
Hypotheses (nz_p : p != 0) (px_0 : root (p ^ iota) x).
Let inFz z w := exists q, (q ^ iota).[z] = w.

Lemma large_field_PET q :
root (q ^ iota) y -> separable_poly q ->
exists2 r, r != 0
& forall t (z := iota t * y - x), ~~ root r (iota t) -> inFz z x /\ inFz z y.