1. F. Ardila, T. Bliem, D. Salazar, Gelfand-Tsetlin polytopes and Feigin-Fourier-Littelmann-Vinberg polytopes as marked poset polytopes, arXiv:1008.2365.
2. N. Bourbaki, Groupes et Algèbres de Lie, Chaps. IV, V, VI, Actualités Scientifiques et Industrielles, No. 1337, Hermann, Paris, 1968. Russian transl.: Н. Бурбаки, Груnnы u алгебры Лu, гл. IV, V, VI, Мир, M., 1972.
3. R.-K. Brylinski, Limits of weight spaces, Lusztig's q-analogs and fiberings of adjoint orbits, J. Amer. Math. Soc. 2 (1989), no. 3, 517–533.
4. E. Feigin, The PBW filtration, Represent. Theory 13 (2009), 165–181.
5. E. Feigin, The PBW filtration, Demazure modules and toroidal current algebras, SIGMA 4 (2008), 070, 21 pp.