question type TOC/Automata Languages

1 What does it mean that a CFG is ambiguous? Consider the following CFG:

Op1 Op1 + Op2 | Op1 - Op2 | Op2; Op2 Op2 * Expr | Op2 / Op2 | Expr; Expr ( Op1 ) | id,

where the terminals are {(,),+,-,*,/,id} and Op1 is the starting symbol. This grammar defines well-bracketed mathematical expressions that have addition, subtraction, multiplication, and division as operations. For example,

( id + id ) / id - id * id

is a string that can be generated by the grammar. Is this grammar ambiguous? Justify your answer.

[10 marks]