English
As before, IsFiniteLength(R,M) is equivalent to the existence of a composition series of Submodules of M with head ⊥ and last ⊤.
Русский
Как и прежде, конечная длина модуля эквивалентна существованию композиционной серии подсистем M с головой ⊥ и последним ⊤.
LaTeX
$$$\\operatorname{IsFiniteLength} R M \\iff \\exists s : CompositionSeries (Submodule R M), s.head = \\bot \\land s.last = \\top$$$
Lean4
theorem isFiniteLength_iff_exists_compositionSeries :
IsFiniteLength R M ↔ ∃ s : CompositionSeries (Submodule R M), s.head = ⊥ ∧ s.last = ⊤ :=
⟨fun h ↦
have ⟨_, _⟩ := isFiniteLength_iff_isNoetherian_isArtinian.mp h
exists_compositionSeries_of_isNoetherian_isArtinian R M,
isFiniteLength_of_exists_compositionSeries⟩