want to know there's an input which makes the circuit print one right then you can prove that you you would need to call this black box at least to the end times to know for sure by there ways you could trip up any particular strategy for querying this black box getting inputs and outputs without looking in it so that you've got to take to the end time so if we can solve the problem into the end over a ten time then there is some fundamental way in which we are opening up the guts of this circuit and getting some advantage over a black box