The set of tokens of the language is {+,*,(,),NUMBER}. The token NUMBER represents unsigned integers, i.e., non-empty sequences of digits. The expressions 1, 2*(3+4), (5+6)*7+8 and 0*(2+1)*0+1 are correct but *, )2+, +(*), 1 2, *4, ()), 1*1*(2*) are not. The generated AST must have at most one symbol + at the root of every sum, and a single * at the root of every product. The usual precedence of * over + applies, and parentheses are allowed. For example, for input 1+2+3*(4+5+6)*7 the resulting AST must be +(1,2,*(3,+(4,5,6),7)), whereas 1 has AST 1 and 1*2*3 has AST *(1,2,3).