English
If p is separable over R and f: R →+* S is a ring homomorphism, then the image p.map f is separable over S.
Русский
Если p разделим над R и f: R →+* S — гомоморфизм колец, то полином p.map f разделим над S.
LaTeX
$$$\\operatorname{Separable}(p) \\Rightarrow \\operatorname{Separable}(p\\map f)$$$
Lean4
theorem map {p : R[X]} (h : p.Separable) {f : R →+* S} : (p.map f).Separable :=
let ⟨a, b, H⟩ := h
⟨a.map f, b.map f, by
rw [derivative_map, ← Polynomial.map_mul, ← Polynomial.map_mul, ← Polynomial.map_add, H, Polynomial.map_one]⟩