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Let G be a CFG , l be the number of left most derivations , r be the number of right most derivations and p be the number of parse trees.Assume l , p , r are computed for a particular string . For a given CFG 'G' and given string 'w'. What is the relation between l , p and r

a) l <=p<=r



in Compiler Design 435 views
For unambiguous grammar b)
Please explain.

both lmd and rmd trees are parse trees. For any unambiguous grammar we have unique lmd and rmd. Hence l = r.

and parse trees are l + r.

Correct me if I’m wrong .


L =r   means left most derivation and right most derivation is same

so which means there is only one parse tree possible

so l=p=r


is when its ambiguous and we have more than one left and right most derivations

1 Answer

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For a particular string, there can be just one Leftmost derivation, and just one Rightmost derivation. So, l = r.

Now, both the derivations translate into the same parse tree. But in case of ambiguous grammars, there can be more than one parse trees. However, RMD and LMD for a particular string remain just one.

Hence, l = r $\leq$ p

So, none of the above.

Option D.


Assuming the grammar is unambiguous, Option B.

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