This exercise does the EMDAS part of PEMDAS. That is, it gives you a function, pemdas_operator(ops, items), that will allow you to do the EMDAS part. Consider the MD part. The idea is that in "3+4*5", we do MD (multiplication and division) before AS (addition and subtraction). This transforms "3+4*5" into "3+(4*5)". In our notation, using a list of items, pemdas_operator(['*', '/'], [3, '+', 4, '*', 5]) should return [3, '+', [4, '*', 5]].