∀ {R : Type u_1} {M : Type u_2} [inst : Semiring R] [inst_1 : AddCommMonoid M] [inst_2 : Module R M] {s : Finset M}
  {x : M}, (x ∈ Submodule.span R ↑s) = ∃ f, Function.support f ⊆ ↑s ∧ ∑ a ∈ s, f a • a = x