English
If A is a subsingleton ring, then the resolvent set of any a ∈ A is the entire base, i.e., resolventSet(R,a) = S univ (equivalently every r ∈ R lies in the resolvent set of a).
Русский
Если A —Подмножество (субоднородное) кольцо, то резольвентное множество любого элемента a ∈ A является всем основанием: resolventSet(R,a) = S univ.
LaTeX
$$$\operatorname{resolventSet}(R,a) = \mathrm{Set.univ}$$$
Lean4
@[simp]
theorem resolventSet_of_subsingleton [Subsingleton A] (a : A) : resolventSet R a = Set.univ := by
simp_rw [resolventSet, Subsingleton.elim (algebraMap R A _ - a) 1, isUnit_one, Set.setOf_true]