then we start with formula_25, and can choose a rule to apply to it. if we choose rule 1, we replace formula_25 with formula_30 and obtain the string formula_30. if we choose rule 1 again, we replace formula_25 with formula_30 and obtain the string formula_34. this process is repeated until we only have symbols from the alphabet (i.e., formula_23 and formula_24). if we now choose rule 2, we replace formula_25 with formula_38 and obtain the string formula_39, and are done. we can write this series of choices more briefly, using symbols: formula_40. the language of the grammar is the set of all the strings that can be generated using this process: formula_41.