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An unambiguous grammar has same leftmost and rightmost derivation.

True or False

and how??

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"An unambiguous grammar has same leftmost and rightmost derivation"

This statement is false, let me take an example, suppose given gammer is (which is certainly unambiguous)

S -> AB
A -> a
B -> b

Suppose our input string is ab

Left Most Derivation
S -> AB -> aB -> ab

Right Most Derivation
S -> AB -> Ab -> ab

Notice Left Most derivation and Right most derivation are not same, still gammer is unambiguous.

Here is the Derivation Tree

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