Describe all the viable prefixes for the following grammars:
- The grammar $S\rightarrow 0S1\mid 01$ of Question $4.2.2(a)$.
- The grammar $S\rightarrow SS+\mid SS\ast\mid a$ of Question $4.2.1$.
- The grammar $S\rightarrow S(S)\mid \epsilon$ of Question $4.2.2(c)$.