Solution
= Solution
False. Let $\lambda=(3)$, $e=2$, and $f=3$. Then
$$
C_2(C_3(\lambda))=C_2(\varnothing)=\varnothing,
\qquad
C_3(C_2(\lambda))=C_3((1))=(1).
$$
Thus core operations for different moduli need not commute.
= Solution
False. Let $\lambda=(3)$, $e=2$, and $f=3$. Then
$$
C_2(C_3(\lambda))=C_2(\varnothing)=\varnothing,
\qquad
C_3(C_2(\lambda))=C_3((1))=(1).
$$
Thus core operations for different moduli need not commute.