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I have an indirect left recursive grammar: expr_1 := expr_1 ...

expr_1 := `not`expr | expr_2
 expr_2 := expr_3 or expr_2 | expr_3
 expr_3 := expr_4 and expr_3 | expr_4
 expr_4 := expr_1 `if` expr_1 `else` expr_5 | expr_5
 expr_5 := expr_1

I do not understand why the algorithm https://en.wikipedia.org/wiki/Left_recursion works and what ordering I should choose.

Edit: I will try the reverse ordering now.

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  • $\begingroup$ I would suggest you first dry-run the algorithm on your example grammar and possibly try a few more. Then the rationale behind the algorithm would be clear. You can also find explanations in the standard textbooks as well. $\endgroup$
    – codeR
    Commented May 17 at 11:09

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