English
The rank of L equals the natTrailingDegree of the characteristic polynomial of ad_R L.
Русский
Ранг Ли-алгебры L равен natTrailingDegree характеристического многочлена ад_R L.
LaTeX
$$$$ \\operatorname{rank}_R L = (\\operatorname{polyCharpoly} (\\operatorname{ad} R L).toLinearMap b).\\operatorname{natTrailingDegree} $$$$
Lean4
theorem finrank_engel (x : L) : finrank K (engel K x) = (ad K L x).charpoly.natTrailingDegree :=
(ad K L x).finrank_maxGenEigenspace_zero_eq