Solution (source code)

= Solution

If $h=aga^{-1}$, the representation law gives $D(h)=D(a)D(g)D(a)^{-1}$. Trace invariance under this <similarity transformation> gives
$$
\boxed{\chi_D(h)=\chi_D(g).}
$$
Thus the <character of a representation> is constant on every <conjugacy class>.