English
If f: M → N is a nonzero map, there exists a submodule S ⊆ M such that N is linearly isomorphic to S.
Русский
Если существует ненулевое отображение f: M → N, то существует подмодуль S ⊆ M с \(N \cong S\).
LaTeX
$$$[IsSemisimpleModule R M] \\Rightarrow \\exists S:\\ Submodule R M, \\, Nonempty (N \\cong S).$$$
Lean4
theorem linearEquiv_of_ne_zero [IsSemisimpleModule R M] [IsSimpleModule R N] {f : M →ₗ[R] N} (h : f ≠ 0) :
∃ S : Submodule R M, Nonempty (N ≃ₗ[R] S) :=
have ⟨m, (_ : IsSimpleModule R m), ne⟩ :=
exists_ne_zero_of_sSup_eq_top h _ (IsSemisimpleModule.sSup_simples_eq_top ..)
⟨m, ⟨.symm <| .ofBijective _ ((bijective_or_eq_zero _).resolve_right ne)⟩⟩