English
If M is a semisimple module over R, then its Jacobson radical is the zero submodule.
Русский
Если M — полупростой модуль над R, то его радикал Якобсона равен нулю.
LaTeX
$$Module.jacobson R M = ⊥$$
Lean4
theorem jacobson_eq_bot [IsSemisimpleModule R M] : Module.jacobson R M = ⊥ :=
have ⟨s, e, simple⟩ := isSemisimpleModule_iff_exists_linearEquiv_dfinsupp.mp ‹_›
let f : M →ₗ[R] ∀ m : s, m.1 := (LinearMap.pi DFinsupp.lapply).comp e.toLinearMap
Module.jacobson_eq_bot_of_injective f (DFinsupp.injective_pi_lapply (R := R).comp e.injective)
(Module.jacobson_pi_eq_bot _ _ fun i ↦ IsSimpleModule.jacobson_eq_bot R _)