English
The decomposition subgroup is defined as the stabilizer in the automorphism group of the field action on valuation subrings.
Русский
Декомпозиционная подгруппа определяется как стабилизатор в группе аутоморфизмов поля действия на оценочные подкольца.
LaTeX
$$$\\mathrm{decompositionSubgroup}(A) := \\mathrm{Stabilizer}_{L/K}(A)\\subseteq \\mathrm{Aut}_K(L)$ for a valuation subring A.$$
Lean4
/-- If `hJ : J ⊆ supp v` then `onQuotVal hJ` is the induced function on `R / J` as a function.
Note: it's just the function; the valuation is `onQuot hJ`. -/
def onQuotVal {J : Ideal R} (hJ : J ≤ supp v) : R ⧸ J → Γ₀ :=
Valuation.onQuotVal v hJ