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$\DeclareMathOperator\Ind{Ind}$Let $d = d_1 + d_2$ with $d_1$, $d_2$ positive integers. Let $\lambda$ be a partition of $d_1$ and $\mu$ a partition of $d_2$, so that the Young symmetrizer construction ...

Throughout this post $R$ denotes a discrete valuation ring with residue field $R/\frak{m}$ being finite. I'm reading Macdonald's exposition on the Hall Algebra on page 183 and trying to make sense of ...