English
Inserting zero into a set does not change its span: span R (insert 0 s) = span R s.
Русский
Добавление нуля к множеству не изменяет его span: span R (insert 0 s) = span R s.
LaTeX
$$$ \operatorname{span} R (\operatorname{insert}(0 : M)\, s) = \operatorname{span} R s. $$$
Lean4
@[simp]
theorem span_insert_zero : span R (insert (0 : M) s) = span R s :=
by
refine le_antisymm ?_ (Submodule.span_mono (Set.subset_insert 0 s))
rw [span_le, Set.insert_subset_iff]
exact ⟨by simp only [SetLike.mem_coe, Submodule.zero_mem], Submodule.subset_span⟩