“…In contrast to this situation, for nonsemisimple Lie algebras, very little is known. Apart from the main result of [8], which, in addition to , classifies simple modules over the Borel subalgebra of , several special classes of simple modules were studied for various specific nonsemisimple Lie algebras (see, e.g., [6], [7], [10], [11], [20], [39], [43], [52] and references therein). We now look at some of these and some other results in more detail.…”