# Need for an augmented grammar

The question is under the concept of LR parser. Suppose the original grammar is
S->AA
A->aA|b

Is it necessary to add an additional rule S'->S to make it as augmented grammar? In short, I want to know the use of augmented grammar.

• The title you have chosen is not well suited to representing your question. Please take some time to improve it; we have collected some advice here. Thank you! – Raphael Apr 8 '16 at 10:49

Yes, if you follow the canonical conversion of augmented grammars, a first step is adding a new start symbol $S'$ and the production $S' \to S$, since the algorithm may later "change" $S$.