English
If R is not a field and M is maximal, then ⊥ < M.
Русский
Если R не является полем и M — максимальный идеал, то ⊥ < M.
LaTeX
$$$\\bot < M$$$
Lean4
theorem bot_lt_of_maximal (M : Ideal R) [hm : M.IsMaximal] (non_field : ¬IsField R) : ⊥ < M :=
by
rcases Ring.not_isField_iff_exists_ideal_bot_lt_and_lt_top.1 non_field with ⟨I, Ibot, Itop⟩
constructor; · simp
intro mle
apply lt_irrefl (⊤ : Ideal R)
have : M = ⊥ := eq_bot_iff.mpr mle
rw [← this] at Ibot
rwa [hm.1.2 I Ibot] at Itop