One parse tree only a The role of the grammar a distinguish between syntactically legal and illegal programs a But that's not enough: it must also define a parse tree a the parse tree conveys the meaning of the program What if a string can be parsed with multiple parse trees? a we say the grammar is ambiguous a must fix the grammar(the problem is not in the parser) a Note: often a string can be derived in more than one way D ie, with more than one derivation sequence o this does not mean the grammar is ambiguous
