English
A subfield of an ordered field is itself an ordered field (with the inherited order).
Русский
Подполе упорядоченного поля само является упорядованным полем (с наследуемым порядком).
LaTeX
$$$\text{If } K \text{ is an ordered field and } S \subseteq K \text{ is a subfield, then } S \text{ inherits an ordered field structure.}$$$
Lean4
/-- A subfield of an ordered field is a ordered field. -/
instance toIsStrictOrderedRing [Field K] [LinearOrder K] [IsStrictOrderedRing K] (s : Subfield K) :
IsStrictOrderedRing s :=
Function.Injective.isStrictOrderedRing Subtype.val rfl rfl (fun _ _ => rfl) (fun _ _ => rfl) .rfl .rfl