English
Sum of a multiset of elements in a nonunital subring is in the nonunital subring.
Русский
Сумма мультисетa элементов в неумножающем подкольце принадлежит ему.
LaTeX
$$$\\forall s: \\text{NonUnitalSubring } R\\, (m: \\text{Multiset } R),\\ (\\forall a \\in m, a \\in s) \\Rightarrow m.sum \\in s$$$
Lean4
/-- Sum of a multiset of elements in a `NonUnitalSubring` of a `NonUnitalRing` is
in the `NonUnitalSubring`. -/
protected theorem multiset_sum_mem {R} [NonUnitalNonAssocRing R] (s : NonUnitalSubring R) (m : Multiset R) :
(∀ a ∈ m, a ∈ s) → m.sum ∈ s :=
multiset_sum_mem _