For a permutation Formula: see text in the symmetric group Formula: see text, let Formula: see text denote the simple highest weight module in the principal block of the BGG category Formula: see text for the Lie algebra Formula: see text. We first prove that Formula: see text is Kostant negative whenever Formula: see text consecutively contains certain patterns. We then provide a complete answer to Kostant’s problem in type Formula: see text and show that the indecomposability conjecture also holds in type Formula: see text, that is, applying an indecomposable projective functor to a simple module outputs either an indecomposable module or zero.
Mazorchuk et al. (Fri,) studied this question.