# Intertwining number

If $\pi_1$ and $\pi_2$ are irreducible and finite dimensional or unitary, then the intertwining number $c(\pi_1,\pi_2)$ is equal to $1$ or $0$, depending on whether $\pi_1$ and $\pi_2$ are equivalent or not.
$\pi_1$ and $\pi_2$ are representations of a finite group $G$ over a field $K$. Why is there an "or unitary"? Is this true if the representations are just irreducible and finite-dimensional, but $K$ not a splitting field?
As it seams to be wrong, if $\pi_i$ are not absolutely irreducible, how is it possible to determine $\dim_K(\operatorname{Hom}_{K[G]}(\pi)$ if $\pi$ is irreducible, but $K$ not a splitting field. Are there theorems when this dimension is 1?