question set

Question

An unambiguous grammar has same leftmost and rightmost derivation.

True or False

and how??

Comments

Ambiguity has no relation with left most and right most derivation.It is true.Every grammer if it has some string then it will have both left and right deravation

Answer 1

"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