Arguments map_poly_inj {F R} f [p1 p2] : rename.
Section MaxRoots.
Variable R : unitRingType.
Implicit Types (x y : R) (rs : seq R) (p : {poly R}).
Definition diff_roots (x y : R) := (x * y == y * x) && (y - x \in GRing.unit).
Fixpoint uniq_roots rs :=
if rs is x :: rs' then all (diff_roots x) rs' && uniq_roots rs' else true.

Lemma uniq_roots_prod_XsubC p rs :
all (root p) rs -> uniq_roots rs ->
exists q, p = q * \prod_(z <- rs) ('X - z%:P).