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Here S is the non-terminal start symbol; A, B, C are non-terminal symbols; x, y, are terminal symbols

S → A B A C | A C A B
A → A x | A y
B → B x x | B y y
C → x y | y x

Having watched videos I understand simple examples for eliminating left recursion in production rules such as 

S → a S a
S → b S b
S → ε

but I don't understand how to eliminate left recursion in the rules shown above. Can anyone explain or point me in the direction of an explanation?

rici
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James
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  • @Rishav This is not a question without code. The 'code' is the grammar which the OP provided. There is nothing here that constitutes a bad question. Best not to comment on questions outside your areas of expertise. – user207421 May 08 '18 at 21:33
  • @EJP Okay. Sorry. Will keep that in mind. I just thought that questions wanting an explanation are not so welcomed here from my experience. Ill retract my comment. :) – Rishav May 09 '18 at 05:10
  • @Rishav *All* questions should ask for an explanation. – user207421 May 09 '18 at 22:14

1 Answers1

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There is no left-recursion in your second example, so removing the left-recursion is trivial.

In your first grammar, you need to left-factor before you can tackle elimination of recursion. (Indeed, the title of your question says "left-factor", so you already had this clue in your homework assignment/quiz.)

The link provided above is one of hundreds found by Google with the search term "left factor grammar", but I'd suggest that you at least consider the possibility that your course materials are a better source of information than Google searches (or random Youtube videos).

rici
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