Abstract:
The modules $D^\lambda{\downarrow}_{\Sigma_{n-1}}$ and
$D^\lambda{\uparrow}^{\Sigma_{n+1}}$ are described for certain simple
$K\Sigma_n$-modules $D^\lambda$ (the completely splittable ones or close to them), where $K$ is a field of characteristic $p>0$ and $\Sigma_n$ is the symmetric group of degree $n$. This result is based on an upper bound for the dimensions of the
$\operatorname{Ext}^1$-spaces between certain simple modules.