# Notation

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$(K,\mathcal{O},k)$ is a $p$-modular system, where $\mathcal{O}$ is a complete discrete valuation ring with algebraically closed residue field $k=\mathcal{O}/J(\mathcal{O})$ and $K$ is the field of fractions of $\mathcal{O}$, of characteristic zero. In order to make a consistent choice of $(K,\mathcal{O},k)$ we take $k$ to be the algebraic closure of the field with $p$ elements and $\mathcal{O}$ to be the ring of Witt vectors for $k$ This has the disadvantage that for $G$ a finite group $KG$ need not contain the primitive character idempotents, but this condition can usually be avoided.
In the below, $G$ is a finite group and $B$ is a block of $kG$ or $\mathcal{O}G$ depending on the context.
 $k(B)$ Number of irreducible characters in $B$ $l(B)$ Number of isomorphism classes of simple $B$-modules