English
For a tower of algebras with faithful scalar action and R→S algebraic, an element a ∈ A is algebraic over R if and only if it is algebraic over S.
Русский
Для башни алгебр с верным действием скаляров и при алгебраичности R→S элемент a ∈ A алгебраичен над R тогда и только тогда, когда он алгебраичен над S.
LaTeX
$$$\\IsAlgebraic_R A \\iff \\IsAlgebraic_S A$$$
Lean4
protected theorem isAlgebraic_iff [Algebra.IsAlgebraic R S] [FaithfulSMul R S] {a : A} :
IsAlgebraic R a ↔ IsAlgebraic S a :=
⟨.extendScalars (FaithfulSMul.algebraMap_injective ..), .restrictScalars _⟩