If $L$ is semisimple, how is this ideal of $L$ semisimple?

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From Humphrey's book, page 23:

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In the second paragraph, it is stated that any ideal of $L_1$ is an ideal of $L$. How is this so?

Also, it is stated that this implies $L_1$ is semisimple. How is this so?

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The first question has already been answered before.

Concerning the other question, let $\mathfrak a$ be a solvable ideal of $L_1$. Then it is a solvable ideal of $L$. But $L$ is semisimple, which means that its only solvable ideal is $\{0\}$. So, $\mathfrak a=\{0\}$, which proves that $L_1$ is semisimple.