English
A stability equivalence for Finset: membership in stabilizer is characterized by a condition on all elements.
Русский
Эквивалентность принадлежности стабилизатору Finset через условие на все элементы.
LaTeX
$$$ a \in \operatorname{Stabilizer}_G(s) \iff \forall b, b \in s \Rightarrow a \cdot b \in s \ \,\land\, b \in s \Rightarrow a \cdot b \in s $$$
Lean4
@[to_additive]
theorem mem_stabilizer_finset {s : Finset α} : a ∈ stabilizer G s ↔ ∀ b, a • b ∈ s ↔ b ∈ s := by
simp_rw [← stabilizer_coe_finset, mem_stabilizer_set, Finset.mem_coe]