Feigin, E.
(Symmetry, Integrability and Geometry: Methods and Applications, 2008)
Let L be the basic (level one vacuum) representation of the affine Kac-Moody Lie algebra ^g. The m-th space Fm of the PBW filtration on L is a linear span of vectors of the form x1¼xlv0, where l ≤ m, xi Î ^g and v0 is a ...