English
For a division ring R and a nonzero R-module M, M is simple if and only if its finite dimension over R is 1.
Русский
Для деления кольца R и немножества модуля M над R, модуль M прост iff его размерность по R равна 1.
LaTeX
$$$\\text{IsSimpleModule } R M \\;\\iff\\; \\dim_R M = 1$$$
Lean4
theorem isSimpleModule_iff_finrank_eq_one {R M} [DivisionRing R] [AddCommGroup M] [Module R M] :
IsSimpleModule R M ↔ Module.finrank R M = 1 :=
⟨fun h ↦
have := h.nontrivial;
have ⟨v, hv⟩ := exists_ne (0 : M)
(finrank_eq_one_iff_of_nonzero' v hv).mpr (IsSimpleModule.toSpanSingleton_surjective R hv),
(isSimpleModule_iff ..).mpr ∘ is_simple_module_of_finrank_eq_one⟩