English
If K is a field and L is a finite type K-algebra which is unramified, then L is a separable algebra over K.
Русский
Если K — поле, L — конечнопредельная над K алгебра, неразветвленная, то L — сепарабельная над K.
LaTeX
$$$[\text{FormallyUnramified } K L] \Rightarrow [\text{IsSeparable } K L]$$$
Lean4
/-- Being unramified is transported via algebra isomorphisms. -/
theorem of_equiv [Unramified R A] (e : A ≃ₐ[R] B) : Unramified R B
where
formallyUnramified := FormallyUnramified.of_equiv e
finiteType := FiniteType.equiv Unramified.finiteType e