Solution
= Solution
True. A hook length divisible by $ef$ is divisible by $e$. If $\lambda$ is its own <Core of a partition> $C_e(\lambda)$, it has no such hook, so it is also its own $ef$-core.
= Solution
True. A hook length divisible by $ef$ is divisible by $e$. If $\lambda$ is its own <Core of a partition> $C_e(\lambda)$, it has no such hook, so it is also its own $ef$-core.