Is it possible for an ambiguous context-free grammar(CFG) to convert into Chomsky Normal Form(CNF) and becomes unambiguous?
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Sure. All you really need is a single example to show this is possible. Consider the ambiguous grammar
S :- A | B
A :- a
B :- a
This grammar is equivalent to the following grammar in CNF
S :- a
This grammar is not ambiguous.

Patrick87
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Is the grammar first ambiguous because "a" has two leftmost derivations (1) A :- a, S :- A and (2) B :- b; S :- B? – sprajagopal Jan 28 '21 at 16:22
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1Yes, two distinct derivations produce the string a: S -> A -> a and S -> B -> a. The parse trees are different but the string derived is the same. – Patrick87 Jan 28 '21 at 16:30