Ambiguity of a context-free Grammer is undecidable means there are some context free grammers where it is impossible to determine if they are ambiguous or not.

Ambiguity of a context-free Grammer is undecidable means there are some context free grammers where it is impossible to determine if they are ambiguous or not. There are context free grammers that we can prove are unambiguous. As an example "A = xAy | ε" is unambiguous. Lojban is one of the examples of grammers we are able to prove is unambiguous.