Refer back to the context-free grammar. Add attribute rules to the grammar to accumulate into the root of the tree a count of the maximum depth to which parentheses are nested in the program string. For example, given the string f1(a, f2(b * (c + (d - (e - f))))), the stmt at the root of the tree should have an attribute with a count of 3 (the parentheses surrounding argument lists don’t count).