“…. , d c } of a nilpotent Lie algebra g with descending central series g (i) = [g, g (i−1) ] is defined, according to the literature beginning with Vergne [20], by the integers d i = dim g (i− 1) g (i) . Nilpotent (real or complex) Lie algebras of type {n, 2} have been classified firstly by Gauger [11], applying the canonical reduction of the pair F 1 , F 2 , but, according to results of Belitskii, Lipyanski, and Sergeichuk [3], it is not possible to carry this argument further.…”