English
For simple modules M,N over R, any linear map f: M → N is either bijective or zero.
Русский
Для простых модулей M,N над R любой линейный отображение либо биективно, либо нулево.
LaTeX
$$$[IsSimpleModule(R,M)][IsSimpleModule(R,N)](f: M \\to N)\\; \\text{isBijectiveOrZero}(f).$$$
Lean4
/-- **Schur's Lemma** for linear maps between (possibly distinct) simple modules -/
theorem bijective_or_eq_zero [IsSimpleModule R M] [IsSimpleModule R N] (f : M →ₗ[R] N) : Function.Bijective f ∨ f = 0 :=
or_iff_not_imp_right.mpr fun h ↦ ⟨injective_of_ne_zero h, surjective_of_ne_zero h⟩