Context Free Grammar for $\{0^n1^n \mid n \geq 0\}^*$ Give a context free grammar for the following language over $\Sigma = \{0,1\}$:
  $ L = L_1^* $
  where $ L_1 = \{0^n1^n : n \geq 0\}$.


Not really sure where to start with this one. Any help is appreciated
Hints:


Start with a context-free grammar for $L_1$.
Modify it to a context-free grammar for $L = L_1^*$. There is a simple transformation which works for any context-free language $L_1$ and any context-free grammar generating it.